diff --git a/README.md b/README.md
index fba05c2..062b217 100644
--- a/README.md
+++ b/README.md
@@ -136,123 +136,180 @@ Here, the %PDI \ref trace_plugin "Trace plugin" is used to trace %PDI calls.
 Notice that some share/reclaim pairs come one after the other while others are
 interlaced.
 Is one better than the other?
-If you do not know the answer to this question, just wait until Ex5. :)
+If you do not know the answer to this question, just wait until ex5. :)
 
 
 ## Decl'HDF5 plugin
 
+From exercise 3 to exercise 9 included, we present the \ref Decl_HDF5_plugin 
+"Decl'HDF5 plugin" (`decl_hdf5`). We will introduce some keywords (`when`, 
+`datasets`, ...) in the sub-tree of `decl_hdf5` in configuration YAML file.
+
+All keywords are defined in the last section **full configuration example** of 
+\ref Decl_HDF5_plugin "Decl'HDF5 plugin".
+
 ### Ex3. HDF5 through PDI
 
-In this exercise, the code is the same as in ex2.
-No need to touch the C code here, modification of the YAML file (`ex3.yml`)
-should be enough.
+In this exercise, the C code is the same as in ex2. You only need to modify the 
+YAML file (`ex3.yml`).
 
 * Examine the YAML file, compile the code and run it.
 
-The \ref trace_plugin "Trace plugin" (`trace`) was replaced by the
-\ref Decl_HDF5_plugin "Decl'HDF5 plugin" (`decl_hdf5`) in the specification
-tree.
-In its configuration, the `dsize` variable is written.
+The \ref Decl_HDF5_plugin "Decl'HDF5 plugin" (`decl_hdf5`) is added in the
+specification tree. 
+In its configuration, the `dsize` variable is defined as a metadata for %PDI.
 
-* Write the `psize` and `pcoord` variables in addition to `dsize` to match the
-  content expected as described in the `ex3.h5dump` text file (use the `h5dump`
-  command to see the content of your HDF5 output file in the same format as the
-  `.h5dump` file). You can easily check if the files are the same by running the
-  command:
-```bash
-  diff ex3.h5dump <(h5dump ex3*.h5)
-```
+* Write the `psize` and `pcoord` variables in addition to `dsize` in a file `ex3.h5`
+with one MPI process.
+To achieve this result, you will need to fill 2 sections in the YAML file:
 
-To achieve this result, you will need to fill 2 sections in the YAML file.
+  1. The `data` section to indicate to %PDI the \ref datatype_node "type" of the 
+  fields that are exposed.
 
-1. The `data` section to indicate to %PDI the \ref datatype_node type of the
-   fields that are exposed.
+  2. The `decl_hdf5` section for the configuration of the \ref Decl_HDF5_plugin
+  "Decl'HDF5 plugin".
 
-2. The `decl_hdf5` section for the configuration of the
-   \ref Decl_HDF5_plugin "Decl'HDF5 plugin".
+* Use the `h5dump` command to see the content of your HDF5 output file in the 
+same format as the h5dump file `ex3.h5dump`. You can easily check if the files 
+are the same by running:
+```bash
+  diff ex3.h5dump <(h5dump ex3*.h5)
+```
+To see your `h5` file in readable file format, you can check the section
+[Comparison with the `h5dump` command](#h5comparison).
 
 \warning
-If you relaunch the executable, remember to delete your old `ex3.h5` file
-before, otherwise the data will not be changed.
+If you relaunch the executable, remember to delete your old `ex3.h5` file before,
+otherwise the data will not be changed.
 
 \warning
-Since we write to the same location independently of the MPI rank, this exercise
-will fail if more than one MPI rank is used.
-
+When more than one MPI rank is used, we write to the same location in the file
+independently of the MPI rank. For this reason, this exercise will fail. The next
+exercise solves this issue.
 
 ### Ex4. Writing some real data
 
 In this exercise each MPI process will write its local 2D array block contained
 in the `main_field` variable to a separate HDF5 file.
-Once again, this can be done by modifying the YAML file only, no nee to touch
+Once again, this can be done by modifying the YAML file only, no need to touch
 the C file.
 
 * Examine the YAML file, compile the code and run it.
 
-Look at the number of blocks, you will have to use the correct number of MPI
-ranks to run the example.
-
-Notice that in the YAML file, a list was used in the `decl_hdf5` section with
-multiple write blocks instead of a single one as before in order to write to
-multiple files.
+\note Notice that in the YAML file `ex4.yml`, a list was used in the `decl_hdf5`
+section with multiple write blocks instead of a single one as before in order
+to write to multiple files.
+
+\note Notice that we have moved fields (`dsize`, `psize` and `pcoord`) in the 
+`metadata` section.
+```yaml
+pdi:
+  metadata: # small values for which PDI keeps a copy
+    #*** add ii as metadata
+    #...
+    dsize: { type: array, subtype: int, size: 2 }
+```
+You can reference them from dynamic "$-expressions" in the configuration file.
 
-Also notice that this example now runs in parallel with two processes.
-Therefore it uses "$-expressions" to specify the file names and ensure we
-do not write to the same file from distinct ranks.
+\remark Also notice that this example now runs in parallel with 4 processes.
+To ensure we do not write to the same file, we need  to specify the file name
+using "$-expressions" for the different process rank. 
 
 Unlike the other fields manipulated until now, the type of `main_field` is not
-fully known, its size is dynamic.
-By moving other fields in the `metadata` section, you can reference them from
-"$-expressions" in the configuration file.
+fully known, its size is dynamic. Therefore, we need to define the size in YAML
+file for %PDI using "$-expressions".
 
-* Use a $-expression to specify the size of `main_field`.
+* Describe the temperature data on the current iteration by using a $-expression
+to specify the size of `main_field` in `data` section.
 
-Unlike the other fields manipulated until now, `main_field` is exposed multiple
+Unlike the other fields manipulated until now, `main_field` is exposed multiple 
 times along execution.
-In order not to overwrite it every time it is exposed, you need to add a `when`
-condition to restrict its output.
+In order not to overwrite it every time it is exposed, you propose to write one
+file per rank only at the first iteration (`ii=1`) with the directive `when`.
+
+* Add the iteration loop `ii` as a metadata.
+* Write the curent temperature field in one file per process at first iteration.
 
-* Only write `main_field` at the second iteration (when `ii=1`) and match the
-  expected content as described in `ex4.h5dump`.
+You should be able to match the expected output described in `ex4.h5dump`.
+You can easily check if the files are the same by running:
 ```bash
-  diff ex4.h5dump <(h5dump ex4*.h5)
+  diff ex4.h5dump <(h5dump ex4-data-*.h5)
 ```
+To see your `h5` file in readable file format, you can check the section
+[Comparison with the `h5dump` command](#h5comparison).
 
-### Ex5. Introducing events
+\note A definition of `metadata` and `data` can be:
 
-In ex4., two variables were written to `ex4-data*.h5`, but the file was opened
+- `metadata`: small values for which PDI keeps a copy. These value can be referenced
+by using "$-expressions" in the configuration YAML file.
+
+- `data`    : values for which PDI does not keep a copy.
+
+### Ex5. Introducing events and group of dataset
+
+This exercise is done sequentially to facilitate the comparison between logs.
+
+#### Ex 5.1 PDI event and on_event
+
+In ex4, two variables were written to `ex4-data-*.h5`, but the files were opened
 and closed for each and every write.
+
 Since Decl'HDF5 only sees the data appear one after the other, it does not keep
-the file open.
-Since `ii` and `main_field` are shared in an interlaced way, they are both
-available to %PDI at the same time and could be written without opening the file
-twice.
-You have to use events for that, you will modify both the C and YAML file.
+the file open. Since `ii` and `main_field` are shared in an interlaced way, they
+are both available to %PDI at the same time and could be written without opening 
+the file twice.
+You have to use events for that, you will modify both the C and YAML file in this
+exercise.
 
 * Examine the YAML file and source code.
-
-* In the C file, trigger a %PDI event named `loop` when both `ii` and
+* In the C file, add a %PDI event named `loop` when both `ii` and
   `main_field` are shared.
-  With the \ref trace_plugin "Trace plugin", check that the event is indeed
-  triggered at the expected time as described in `ex5.log` (only the lines
-  matching `[Trace-plugin]` have been kept). You can check if the files are the
-  same by running:
+
+  With the \ref trace_plugin "Trace plugin", check that the event is indeed 
+  triggered at the expected time as described in `ex5.log` (only the lines 
+  matching `[Trace-plugin]` have been kept).
+  Using the previous section [Execution with storage of the log](#execution-with-storage-of-the-log),
+  run  this exercise in saving the output log in the `ex5.result.log`.
+  After that you can easily check if the files are the same by running:
 ```bash
   diff ex5.log <(grep Trace-plugin ex5.result.log)
 ```
+* In the YAML file, use the `on_event` mechanism to trigger the write of `ii` and
+ `main_field` for event `loop` only. This mechanism can be combined with a `when`
+ directive, in that case the write is only executed when both mechanisms agree.
+* Add the `when` directive to write only at iteration 1 and 2. Use the symbol `&` 
+  which corresponds to the logical operation `and`.
+
+#### Ex 5.2 group of dataset
+In ex4, the name of the datasets of `.h5` file are `ii` and `main_field`(see ex4.h5dump).
+Using the keyword `dataset`, it is possible to have a different name from the 
+%PDI variable name.
+
+The name of the dataset is given after the definition of the data 
+```yaml
+       write:
+          ii: # name of the PDI data to write
+            dataset: 'new_name' 
+```
+Using this mechanism, it is possible to define a group object of hdf5 see
+https://support.hdfgroup.org/documentation/hdf5/latest/_h5_g__u_g.html.
+If you want to add a dataset `my_data` in the sub-group `groupA` of the group 
+`my_group`, the name of the dataset will be:
+```yaml
+dataset: 'my_group/groupA/my_data'.
+```
+where the symbol "/" is used to separate groups in path.
 
-* Use the `on_event` mechanism to trigger the write of `ii` and `main_field`.
-  This mechanism can be combined with a `when` directive, in that case the
-  write is only executed when both mechanisms agree.
+* Change the YAML file to write `main_field` and `ii` at iterations 1 and 2,
+in two distinct groups `iter1` and `iter2`.
 
-* Also notice the extended syntax that make it possible to write data to a
-  dataset whose name differs from the %PDI variable name.
-  Use this mechanism to write `main_field` at iterations 1 and 2, in two
-  distinct groups `iter1` and `iter2`.
-  Your output should match the content described in `ex5.h5dump`.
+  To match the expected output described in `ex5.h5dump`. You can easily check
+  if the files are the same by running:
 ```bash
-  diff ex5.h5dump <(h5dump ex5*.h5)
+  diff ex5.h5dump <(h5dump ex5-data-*.h5)
 ```
+  To see your `h5` file in readable file format, you can check the section
+  [Comparison with the `h5dump` command](#h5comparison).
 
 
 ### Ex6. Simplifying the code
diff --git a/ex3.c b/ex3.c
index a2d3a90..aad7ba6 100644
--- a/ex3.c
+++ b/ex3.c
@@ -44,13 +44,32 @@ int pcoord[2];
 /// the alpha coefficient used in the computation
 double alpha;
 
+double L=1.0;
+double source1[4]={0.4, 0.4, 0.2, 100};
+double source2[4]={0.7, 0.8, 0.1, 200};
+
 /** Initialize the data all to 0 except for the left border (XX==0) initialized to 1 million
  * \param[out] dat the local data to initialize
  */
 void init(double dat[dsize[0]][dsize[1]])
 {
 	for (int yy=0; yy<dsize[0]; ++yy)  for (int xx=0; xx<dsize[1]; ++xx)  dat[yy][xx] = 0;
-	if ( pcoord[1] == 0 ) for (int yy=0; yy<dsize[0]; ++yy)  dat[yy][0] = 1000000;
+	double dy = L / ((dsize[0]-2) *psize[0]) ;
+	double dx = L / ((dsize[1]-2) *psize[1]) ;
+
+	double cpos_x,cpos_y;
+	for(int yy=0; yy<dsize[0];++yy) {
+		cpos_y=(yy+pcoord[0]*(dsize[0]-2))*dy-0.5*dy;
+		for(int xx=0; xx<dsize[1];++xx) {
+			cpos_x=(xx+pcoord[1]*(dsize[1]-2))*dx-0.5*dx;
+			if((cpos_y-source1[0])*(cpos_y-source1[0]) + (cpos_x-source1[1])*(cpos_x-source1[1]) <= source1[2]*source1[2]) {
+				dat[yy][xx] = source1[3];
+			}
+			if((cpos_y-source2[0])*(cpos_y-source2[0]) + (cpos_x-source2[1])*(cpos_x-source2[1]) <= source2[2]*source2[2]) {
+				dat[yy][xx] = source2[3];
+			}
+		}
+	}
 }
 
 /** Compute the values at the next time-step based on the values at the current time-step
@@ -60,21 +79,15 @@ void init(double dat[dsize[0]][dsize[1]])
 void iter(double cur[dsize[0]][dsize[1]], double next[dsize[0]][dsize[1]])
 {
 	int xx, yy;
-	for (xx=0; xx<dsize[1]; ++xx) next[0][xx] = cur[0][xx];
 	for (yy=1; yy<dsize[0]-1; ++yy) {
-		next[yy][0] = cur[yy][0];
 		for (xx=1; xx<dsize[1]-1; ++xx) {
-			next[yy][xx] =
-					  (1.-4.*alpha) * cur[yy][xx]
-					+        alpha  * (   cur[yy][xx-1]
-					                    + cur[yy][xx+1]
-					                    + cur[yy-1][xx]
-					                    + cur[yy+1][xx]
-					                  ); 
+			next[yy][xx] = (1.-4.*alpha) * cur[yy][xx]
+					             +alpha  * ( cur[yy][xx-1]
+					                       + cur[yy][xx+1]
+					                       + cur[yy-1][xx]
+					                       + cur[yy+1][xx]); 
 		}
-		next[yy][dsize[1]-1] = cur[yy][dsize[1]-1];
 	}
-	for (xx=0; xx<dsize[1]; ++xx) next[dsize[0]-1][xx] = cur[dsize[0]-1][xx];
 }
 
 /** Exchanges ghost values with neighbours
@@ -104,8 +117,8 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send up
 	MPI_Cart_shift(cart_comm, 0, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send column after ghost
-	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last column (ghost)
+	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send row after ghost
+	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last row (ghost)
 	             cart_comm, &status);
 	
 	// send to the right
@@ -116,7 +129,7 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send to the left
 	MPI_Cart_shift(cart_comm, 1, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1], 1, column, rank_dest,   100, // send column after ghost
+	MPI_Sendrecv(&cur[1][1],          1, column, rank_dest,   100, // send column after ghost
 	             &cur[1][dsize[1]-1], 1, column, rank_source, 100, // receive last column (ghost)
 	             cart_comm, &status);
 }
@@ -162,7 +175,7 @@ int main( int argc, char* argv[] )
 	dsize[1] = global_size[1]/psize[1] + 2;
 	
 	// create a 2D Cartesian MPI communicator & get our coordinate (rank) in it
-	int cart_period[2] = { 0, 0 };
+	int cart_period[2] = { 1, 1 };
 	MPI_Comm cart_comm; MPI_Cart_create(main_comm, 2, psize, cart_period, 1, &cart_comm);
 	MPI_Cart_coords(cart_comm, pcoord_1d, 2, pcoord);
 	
@@ -177,24 +190,20 @@ int main( int argc, char* argv[] )
 	int ii=0;
 	
 	// share useful configuration bits with PDI
-	PDI_share("ii",         &ii,    PDI_OUT);
-	PDI_reclaim("ii");
 	PDI_share("pcoord",     pcoord, PDI_OUT);
 	PDI_reclaim("pcoord");
 	PDI_share("dsize",      dsize,  PDI_OUT);
 	PDI_reclaim("dsize");
 	PDI_share("psize",      psize,  PDI_OUT);
 	PDI_reclaim("psize");
-	PDI_share("main_field", cur,    PDI_OUT);
-	PDI_reclaim("main_field");
 	
 	// the main loop
 	for (; ii<10; ++ii) {
 		// share the loop counter & main field at each iteration
-		PDI_share("ii",         &ii, PDI_OUT);
+		PDI_share("ii", &ii, PDI_OUT);
+		PDI_reclaim("ii");
 		PDI_share("main_field", cur, PDI_OUT);
 		PDI_reclaim("main_field");
-		PDI_reclaim("ii");
 		
 		// compute the values for the next iteration
 		iter(cur, next);
@@ -205,11 +214,10 @@ int main( int argc, char* argv[] )
 		// swap the current and next values
 		double (*tmp)[dsize[1]] = cur; cur = next; next = tmp;
 	}
-	// finally share the main field after the main loop body
-	PDI_share("main_field", cur, PDI_OUT);
-	// as well as the loop counter
-	PDI_share("ii",         &ii, PDI_OUT);
+	// finally share the loop counter and main field after the main loop body
+	PDI_share("ii", &ii, PDI_OUT);
 	PDI_reclaim("ii");
+	PDI_share("main_field", cur, PDI_OUT);
 	PDI_reclaim("main_field");
 	
 	// finalize PDI
diff --git a/ex3.yml b/ex3.yml
index a003454..bbf6048 100644
--- a/ex3.yml
+++ b/ex3.yml
@@ -6,10 +6,15 @@ global_size: { height: 60, width: 12 }
 parallelism: { height: 1, width: 1 }
 # PDI configuration
 pdi:
+  #*** describe the data dsize, psize, pcoord
   data:
-    ii: int
-    dsize: { type: array, subtype: int, size: 2 }
+    dsize: {type: array, subtype: int, size: 2}
+    #... psize
+    #... pcoord
+
   plugins:
+    trace:
     decl_hdf5:
-      file: ex3.h5
-      write: [ dsize , ... ]
+    #*** use the decl_hdf5 plugin to write in the file ex3.h5 the data above (dsize, psize, pcoord)
+    #...
+    
\ No newline at end of file
diff --git a/ex4.c b/ex4.c
index dda8529..566389e 100644
--- a/ex4.c
+++ b/ex4.c
@@ -44,13 +44,32 @@ int pcoord[2];
 /// the alpha coefficient used in the computation
 double alpha;
 
+double L=1.0;
+double source1[4]={0.4, 0.4, 0.2, 100};
+double source2[4]={0.7, 0.8, 0.1, 200};
+
 /** Initialize the data all to 0 except for the left border (XX==0) initialized to 1 million
  * \param[out] dat the local data to initialize
  */
 void init(double dat[dsize[0]][dsize[1]])
 {
 	for (int yy=0; yy<dsize[0]; ++yy)  for (int xx=0; xx<dsize[1]; ++xx)  dat[yy][xx] = 0;
-	if ( pcoord[1] == 0 ) for (int yy=0; yy<dsize[0]; ++yy)  dat[yy][0] = 1000000;
+	double dy = L / ((dsize[0]-2) *psize[0]) ;
+	double dx = L / ((dsize[1]-2) *psize[1]) ;
+
+	double cpos_x,cpos_y;
+	for(int yy=0; yy<dsize[0];++yy) {
+		cpos_y=(yy+pcoord[0]*(dsize[0]-2))*dy-0.5*dy;
+		for(int xx=0; xx<dsize[1];++xx) {
+			cpos_x=(xx+pcoord[1]*(dsize[1]-2))*dx-0.5*dx;
+			if((cpos_y-source1[0])*(cpos_y-source1[0]) + (cpos_x-source1[1])*(cpos_x-source1[1]) <= source1[2]*source1[2]) {
+				dat[yy][xx] = source1[3];
+			}
+			if((cpos_y-source2[0])*(cpos_y-source2[0]) + (cpos_x-source2[1])*(cpos_x-source2[1]) <= source2[2]*source2[2]) {
+				dat[yy][xx] = source2[3];
+			}
+		}
+	}
 }
 
 /** Compute the values at the next time-step based on the values at the current time-step
@@ -60,21 +79,15 @@ void init(double dat[dsize[0]][dsize[1]])
 void iter(double cur[dsize[0]][dsize[1]], double next[dsize[0]][dsize[1]])
 {
 	int xx, yy;
-	for (xx=0; xx<dsize[1]; ++xx) next[0][xx] = cur[0][xx];
 	for (yy=1; yy<dsize[0]-1; ++yy) {
-		next[yy][0] = cur[yy][0];
 		for (xx=1; xx<dsize[1]-1; ++xx) {
-			next[yy][xx] =
-					  (1.-4.*alpha) * cur[yy][xx]
-					+        alpha  * (   cur[yy][xx-1]
-					                    + cur[yy][xx+1]
-					                    + cur[yy-1][xx]
-					                    + cur[yy+1][xx]
-					                  ); 
+			next[yy][xx] = (1.-4.*alpha) * cur[yy][xx]
+					             +alpha  * ( cur[yy][xx-1]
+					                       + cur[yy][xx+1]
+					                       + cur[yy-1][xx]
+					                       + cur[yy+1][xx]); 
 		}
-		next[yy][dsize[1]-1] = cur[yy][dsize[1]-1];
 	}
-	for (xx=0; xx<dsize[1]; ++xx) next[dsize[0]-1][xx] = cur[dsize[0]-1][xx];
 }
 
 /** Exchanges ghost values with neighbours
@@ -104,8 +117,8 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send up
 	MPI_Cart_shift(cart_comm, 0, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send column after ghost
-	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last column (ghost)
+	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send row after ghost
+	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last row (ghost)
 	             cart_comm, &status);
 	
 	// send to the right
@@ -116,7 +129,7 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send to the left
 	MPI_Cart_shift(cart_comm, 1, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1], 1, column, rank_dest,   100, // send column after ghost
+	MPI_Sendrecv(&cur[1][1],          1, column, rank_dest,   100, // send column after ghost
 	             &cur[1][dsize[1]-1], 1, column, rank_source, 100, // receive last column (ghost)
 	             cart_comm, &status);
 }
@@ -162,7 +175,7 @@ int main( int argc, char* argv[] )
 	dsize[1] = global_size[1]/psize[1] + 2;
 	
 	// create a 2D Cartesian MPI communicator & get our coordinate (rank) in it
-	int cart_period[2] = { 0, 0 };
+	int cart_period[2] = { 1, 1 };
 	MPI_Comm cart_comm; MPI_Cart_create(main_comm, 2, psize, cart_period, 1, &cart_comm);
 	MPI_Cart_coords(cart_comm, pcoord_1d, 2, pcoord);
 	
@@ -177,16 +190,12 @@ int main( int argc, char* argv[] )
 	int ii=0;
 	
 	// share useful configuration bits with PDI
-	PDI_share("ii",         &ii,    PDI_OUT);
-	PDI_reclaim("ii");
 	PDI_share("pcoord",     pcoord, PDI_OUT);
 	PDI_reclaim("pcoord");
 	PDI_share("dsize",      dsize,  PDI_OUT);
 	PDI_reclaim("dsize");
 	PDI_share("psize",      psize,  PDI_OUT);
 	PDI_reclaim("psize");
-	PDI_share("main_field", cur,    PDI_OUT);
-	PDI_reclaim("main_field");
 	
 	// the main loop
 	for (; ii<10; ++ii) {
@@ -205,9 +214,8 @@ int main( int argc, char* argv[] )
 		// swap the current and next values
 		double (*tmp)[dsize[1]] = cur; cur = next; next = tmp;
 	}
-	// finally share the main field after the main loop body
+	// finally share the loop counter and main field after the main loop body
 	PDI_share("main_field", cur, PDI_OUT);
-	// as well as the loop counter
 	PDI_share("ii",         &ii, PDI_OUT);
 	PDI_reclaim("ii");
 	PDI_reclaim("main_field");
diff --git a/ex4.h5dump b/ex4.h5dump
index 27a1c5d..99b3b14 100644
--- a/ex4.h5dump
+++ b/ex4.h5dump
@@ -1,4 +1,4 @@
-HDF5 "ex4-data0x0.h5" {
+HDF5 "ex4-data-0x0_iter_1.h5" {
 GROUP "/" {
    DATASET "ii" {
       DATATYPE  H5T_STD_I32LE
@@ -9,45 +9,45 @@ GROUP "/" {
    }
    DATASET "main_field" {
       DATATYPE  H5T_IEEE_F64LE
-      DATASPACE  SIMPLE { ( 32, 14 ) / ( 32, 14 ) }
+      DATASPACE  SIMPLE { ( 32, 8 ) / ( 32, 8 ) }
       DATA {
-      (0,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (1,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (2,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (3,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (4,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (5,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (6,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (7,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (8,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (9,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (10,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (11,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (12,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (13,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (14,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (15,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (16,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (17,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (18,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (19,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (20,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (21,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (22,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (23,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (24,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (25,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (26,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (27,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (28,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (29,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (30,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (31,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+      (0,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (1,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (2,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (3,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (4,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (5,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (6,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (7,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (8,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (9,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (10,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (11,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (12,0): 0, 0, 0, 0, 0, 12.5, 0, 0,
+      (13,0): 0, 0, 0, 0, 12.5, 62.5, 25, 0,
+      (14,0): 0, 0, 0, 0, 25, 87.5, 75, 12.5,
+      (15,0): 0, 0, 0, 12.5, 75, 100, 87.5, 12.5,
+      (16,0): 0, 0, 0, 12.5, 87.5, 100, 87.5, 25,
+      (17,0): 0, 0, 0, 12.5, 87.5, 100, 100, 75,
+      (18,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (19,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (20,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (21,0): 0, 0, 0, 25, 87.5, 100, 100, 87.5,
+      (22,0): 0, 0, 12.5, 75, 100, 100, 100, 87.5,
+      (23,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5,
+      (24,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5,
+      (25,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5,
+      (26,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5,
+      (27,0): 0, 0, 12.5, 75, 100, 100, 100, 87.5,
+      (28,0): 0, 0, 0, 25, 87.5, 100, 100, 87.5,
+      (29,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (30,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (31,0): 0, 0, 0, 12.5, 87.5, 100, 100, 0
       }
    }
 }
 }
-HDF5 "ex4-data1x0.h5" {
+HDF5 "ex4-data-0x1_iter_1.h5" {
 GROUP "/" {
    DATASET "ii" {
       DATATYPE  H5T_STD_I32LE
@@ -58,76 +58,138 @@ GROUP "/" {
    }
    DATASET "main_field" {
       DATATYPE  H5T_IEEE_F64LE
-      DATASPACE  SIMPLE { ( 32, 14 ) / ( 32, 14 ) }
+      DATASPACE  SIMPLE { ( 32, 8 ) / ( 32, 8 ) }
       DATA {
-      (0,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (1,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (2,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (3,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (4,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (5,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (6,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (7,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (8,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (9,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (10,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (11,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (12,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (13,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (14,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (15,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (16,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (17,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (18,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (19,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (20,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (21,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (22,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (23,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (24,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (25,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (26,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (27,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (28,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (29,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (30,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-      (31,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+      (0,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (1,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (2,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (3,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (4,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (5,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (6,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (7,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (8,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (9,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (10,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (11,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (12,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (13,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (14,0): 75, 12.5, 0, 0, 0, 0, 0, 0,
+      (15,0): 87.5, 12.5, 0, 0, 0, 0, 0, 0,
+      (16,0): 87.5, 25, 0, 0, 0, 0, 0, 0,
+      (17,0): 100, 75, 12.5, 0, 0, 0, 0, 0,
+      (18,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (19,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (20,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (21,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (22,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (23,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (24,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (25,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (26,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (27,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (28,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (29,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (30,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (31,0): 0, 87.5, 12.5, 0, 0, 0, 0, 0
       }
    }
 }
 }
-HDF5 "ex4-meta0x0.h5" {
+HDF5 "ex4-data-1x0_iter_1.h5" {
 GROUP "/" {
-   DATASET "dsize" {
+   DATASET "ii" {
       DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
+      DATASPACE  SCALAR
       DATA {
-      (0): 32, 14
+      (0): 1
       }
    }
-   DATASET "psize" {
-      DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
+   DATASET "main_field" {
+      DATATYPE  H5T_IEEE_F64LE
+      DATASPACE  SIMPLE { ( 32, 8 ) / ( 32, 8 ) }
       DATA {
-      (0): 2, 1
+      (0,0): 0, 0, 0, 12.5, 87.5, 100, 100, 0,
+      (1,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5,
+      (2,0): 0, 0, 0, 12.5, 87.5, 100, 100, 75,
+      (3,0): 0, 0, 0, 12.5, 87.5, 100, 87.5, 25,
+      (4,0): 0, 0, 0, 12.5, 75, 100, 87.5, 12.5,
+      (5,0): 0, 0, 0, 0, 25, 87.5, 75, 12.5,
+      (6,0): 0, 0, 0, 0, 12.5, 62.5, 25, 0,
+      (7,0): 0, 0, 0, 0, 0, 12.5, 0, 0,
+      (8,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (9,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (10,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (11,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (12,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (13,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (14,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (15,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (16,0): 25, 0, 0, 0, 0, 0, 0, 0,
+      (17,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (18,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (19,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (20,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (21,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (22,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (23,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (24,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (25,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (26,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (27,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (28,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (29,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (30,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (31,0): 0, 0, 0, 0, 0, 0, 0, 0
       }
    }
 }
 }
-HDF5 "ex4-meta1x0.h5" {
+HDF5 "ex4-data-1x1_iter_1.h5" {
 GROUP "/" {
-   DATASET "dsize" {
+   DATASET "ii" {
       DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
+      DATASPACE  SCALAR
       DATA {
-      (0): 32, 14
+      (0): 1
       }
    }
-   DATASET "psize" {
-      DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
+   DATASET "main_field" {
+      DATATYPE  H5T_IEEE_F64LE
+      DATASPACE  SIMPLE { ( 32, 8 ) / ( 32, 8 ) }
       DATA {
-      (0): 2, 1
+      (0,0): 0, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (1,0): 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+      (2,0): 100, 75, 12.5, 0, 0, 0, 0, 0,
+      (3,0): 87.5, 25, 0, 0, 0, 0, 0, 0,
+      (4,0): 87.5, 12.5, 0, 0, 0, 0, 0, 0,
+      (5,0): 75, 12.5, 0, 0, 0, 0, 0, 0,
+      (6,0): 25, 0, 0, 0, 25, 0, 0, 0,
+      (7,0): 0, 0, 0, 25, 125, 25, 0, 0,
+      (8,0): 0, 0, 0, 25, 150, 50, 0, 0,
+      (9,0): 0, 0, 0, 25, 175, 150, 25, 0,
+      (10,0): 0, 0, 0, 50, 175, 175, 25, 0,
+      (11,0): 0, 0, 25, 150, 200, 175, 25, 0,
+      (12,0): 0, 0, 25, 175, 200, 175, 25, 0,
+      (13,0): 0, 0, 25, 175, 200, 175, 25, 0,
+      (14,0): 0, 0, 25, 150, 200, 175, 25, 0,
+      (15,0): 0, 0, 0, 50, 175, 175, 25, 0,
+      (16,0): 0, 0, 0, 25, 175, 150, 25, 0,
+      (17,0): 0, 0, 0, 25, 150, 50, 0, 0,
+      (18,0): 0, 0, 0, 25, 125, 25, 0, 0,
+      (19,0): 0, 0, 0, 0, 25, 0, 0, 0,
+      (20,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (21,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (22,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (23,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (24,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (25,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (26,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (27,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (28,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (29,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (30,0): 0, 0, 0, 0, 0, 0, 0, 0,
+      (31,0): 0, 0, 0, 0, 0, 0, 0, 0
       }
    }
 }
diff --git a/ex4.yml b/ex4.yml
index 6eed5c6..db060d5 100644
--- a/ex4.yml
+++ b/ex4.yml
@@ -3,20 +3,23 @@ alpha: 0.125
 # global data-size (excluding spacer for boundary conditions or ghosts)
 global_size: { height: 60, width: 12 }
 # degree of parallelism (number of blocks in each dimension)
-parallelism: { height: 2 , width: 1 }
+parallelism: { height: 2 , width: 2 }
 # PDI configuration
 pdi:
   metadata: # small values for which PDI keeps a copy
-    ii: int
+    #*** add ii as metadata
+    #...
     dsize: { type: array, subtype: int, size: 2 }
     psize: { type: array, subtype: int, size: 2 }
     pcoord: { type: array, subtype: int, size: 2 }
   data: # values for which PDI does not keep a copy
-    main_field: { type: array, subtype: double, size: [ "" , "" ] } # we can use $ expressions in type definitions
+    #*** add main_field to the data section, use $-expression to define its size
+    #...
   plugins:
     decl_hdf5:
-      - file: ex4-meta${pcoord[0]}x${pcoord[1]}.h5  # we can use $ expressions in file names
+      #*** write dsize and psize into hdf5, one file per rank
+      - file: ex4-meta-${...}x${...}.h5  # we can use $ expressions in file names
         write: [ dsize, psize ]
-      - file: ex4-data${pcoord[0]}x${pcoord[1]}.h5
-        when: ""  # we can use $-expressions in conditions
-        write: [ ii, main_field ]
+      #*** write main_field and iteration counter into hdf5, one file per rank at first iteration
+      - file: ex4-data-${...}x${...}_iter_${}.h5
+        #...
diff --git a/ex5.c b/ex5.c
index c98ff94..fd676e7 100644
--- a/ex5.c
+++ b/ex5.c
@@ -44,13 +44,32 @@ int pcoord[2];
 /// the alpha coefficient used in the computation
 double alpha;
 
+double L=1.0;
+double source1[4]={0.4, 0.4, 0.2, 100};
+double source2[4]={0.7, 0.8, 0.1, 200};
+
 /** Initialize the data all to 0 except for the left border (XX==0) initialized to 1 million
  * \param[out] dat the local data to initialize
  */
 void init(double dat[dsize[0]][dsize[1]])
 {
 	for (int yy=0; yy<dsize[0]; ++yy)  for (int xx=0; xx<dsize[1]; ++xx)  dat[yy][xx] = 0;
-	if ( pcoord[1] == 0 ) for (int yy=0; yy<dsize[0]; ++yy)  dat[yy][0] = 1000000;
+	double dy = L / ((dsize[0]-2) *psize[0]) ;
+	double dx = L / ((dsize[1]-2) *psize[1]) ;
+
+	double cpos_x,cpos_y;
+	for(int yy=0; yy<dsize[0];++yy) {
+		cpos_y=(yy+pcoord[0]*(dsize[0]-2))*dy-0.5*dy;
+		for(int xx=0; xx<dsize[1];++xx) {
+			cpos_x=(xx+pcoord[1]*(dsize[1]-2))*dx-0.5*dx;
+			if((cpos_y-source1[0])*(cpos_y-source1[0]) + (cpos_x-source1[1])*(cpos_x-source1[1]) <= source1[2]*source1[2]) {
+				dat[yy][xx] = source1[3];
+			}
+			if((cpos_y-source2[0])*(cpos_y-source2[0]) + (cpos_x-source2[1])*(cpos_x-source2[1]) <= source2[2]*source2[2]) {
+				dat[yy][xx] = source2[3];
+			}
+		}
+	}
 }
 
 /** Compute the values at the next time-step based on the values at the current time-step
@@ -60,21 +79,15 @@ void init(double dat[dsize[0]][dsize[1]])
 void iter(double cur[dsize[0]][dsize[1]], double next[dsize[0]][dsize[1]])
 {
 	int xx, yy;
-	for (xx=0; xx<dsize[1]; ++xx) next[0][xx] = cur[0][xx];
 	for (yy=1; yy<dsize[0]-1; ++yy) {
-		next[yy][0] = cur[yy][0];
 		for (xx=1; xx<dsize[1]-1; ++xx) {
-			next[yy][xx] =
-					  (1.-4.*alpha) * cur[yy][xx]
-					+        alpha  * (   cur[yy][xx-1]
-					                    + cur[yy][xx+1]
-					                    + cur[yy-1][xx]
-					                    + cur[yy+1][xx]
-					                  ); 
+			next[yy][xx] = (1.-4.*alpha) * cur[yy][xx]
+					             +alpha  * ( cur[yy][xx-1]
+					                       + cur[yy][xx+1]
+					                       + cur[yy-1][xx]
+					                       + cur[yy+1][xx]); 
 		}
-		next[yy][dsize[1]-1] = cur[yy][dsize[1]-1];
 	}
-	for (xx=0; xx<dsize[1]; ++xx) next[dsize[0]-1][xx] = cur[dsize[0]-1][xx];
 }
 
 /** Exchanges ghost values with neighbours
@@ -104,8 +117,8 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send up
 	MPI_Cart_shift(cart_comm, 0, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send column after ghost
-	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last column (ghost)
+	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send row after ghost
+	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last row (ghost)
 	             cart_comm, &status);
 	
 	// send to the right
@@ -116,7 +129,7 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send to the left
 	MPI_Cart_shift(cart_comm, 1, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1], 1, column, rank_dest,   100, // send column after ghost
+	MPI_Sendrecv(&cur[1][1],          1, column, rank_dest,   100, // send column after ghost
 	             &cur[1][dsize[1]-1], 1, column, rank_source, 100, // receive last column (ghost)
 	             cart_comm, &status);
 }
@@ -162,7 +175,7 @@ int main( int argc, char* argv[] )
 	dsize[1] = global_size[1]/psize[1] + 2;
 	
 	// create a 2D Cartesian MPI communicator & get our coordinate (rank) in it
-	int cart_period[2] = { 0, 0 };
+	int cart_period[2] = { 1, 1 };
 	MPI_Comm cart_comm; MPI_Cart_create(main_comm, 2, psize, cart_period, 1, &cart_comm);
 	MPI_Cart_coords(cart_comm, pcoord_1d, 2, pcoord);
 	
@@ -178,22 +191,21 @@ int main( int argc, char* argv[] )
 	int ii=0;
 	
 	// share useful configuration bits with PDI
-	PDI_share("ii",         &ii,    PDI_OUT);
-	PDI_reclaim("ii");
 	PDI_share("pcoord",     pcoord, PDI_OUT);
 	PDI_reclaim("pcoord");
 	PDI_share("dsize",      dsize,  PDI_OUT);
 	PDI_reclaim("dsize");
 	PDI_share("psize",      psize,  PDI_OUT);
 	PDI_reclaim("psize");
-	PDI_share("main_field", cur,    PDI_OUT);
-	PDI_reclaim("main_field");
+
 	
 	// the main loop
-	for (; ii<10; ++ii) {
+	for (; ii<4; ++ii) {
 		// share the loop counter & main field at each iteration
 		PDI_share("ii",         &ii, PDI_OUT);
 		PDI_share("main_field", cur, PDI_OUT);
+		//*** use PDI_event to prevent redundant open/close of the output file
+		//...
 		PDI_reclaim("main_field");
 		PDI_reclaim("ii");
 		
@@ -206,9 +218,8 @@ int main( int argc, char* argv[] )
 		// swap the current and next values
 		double (*tmp)[dsize[1]] = cur; cur = next; next = tmp;
 	}
-	// finally share the main field after the main loop body
+	// // finally share the loop counter and main field after the main loop body
 	PDI_share("main_field", cur, PDI_OUT);
-	// as well as the loop counter
 	PDI_share("ii",         &ii, PDI_OUT);
 	PDI_reclaim("ii");
 	PDI_reclaim("main_field");
diff --git a/ex5.h5dump b/ex5.h5dump
index 97b38a1..b31c6b5 100644
--- a/ex5.h5dump
+++ b/ex5.h5dump
@@ -12,68 +12,68 @@ GROUP "/" {
          DATATYPE  H5T_IEEE_F64LE
          DATASPACE  SIMPLE { ( 62, 14 ) / ( 62, 14 ) }
          DATA {
-         (0,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (1,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (2,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (3,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (4,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (5,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (6,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (7,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (8,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (9,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (10,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (11,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (12,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (13,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (14,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (15,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (16,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (17,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (18,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (19,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (20,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (21,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (22,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (23,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (24,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (25,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (26,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (27,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (28,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (29,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (30,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (31,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (32,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (33,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (34,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (35,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (36,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (37,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (38,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (39,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (40,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (41,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (42,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (43,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (44,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (45,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (46,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (47,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (48,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (49,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (50,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (51,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (52,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (53,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (54,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (55,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (56,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (57,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (58,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (59,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (60,0): 1e+06, 125000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (61,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+         (0,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (1,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (2,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (3,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (4,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (5,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (6,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (7,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (8,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (9,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (10,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (11,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (12,0): 0, 0, 0, 0, 0, 12.5, 0, 0, 0, 0, 0, 0, 0, 0,
+         (13,0): 0, 0, 0, 0, 12.5, 62.5, 25, 0, 0, 0, 0, 0, 0, 0,
+         (14,0): 0, 0, 0, 0, 25, 87.5, 75, 12.5, 0, 0, 0, 0, 0, 0,
+         (15,0): 0, 0, 0, 12.5, 75, 100, 87.5, 12.5, 0, 0, 0, 0, 0, 0,
+         (16,0): 0, 0, 0, 12.5, 87.5, 100, 87.5, 25, 0, 0, 0, 0, 0, 0,
+         (17,0): 0, 0, 0, 12.5, 87.5, 100, 100, 75, 12.5, 0, 0, 0, 0, 0,
+         (18,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (19,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (20,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (21,0): 0, 0, 0, 25, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (22,0): 0, 0, 12.5, 75, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (23,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (24,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (25,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (26,0): 0, 0, 12.5, 87.5, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (27,0): 0, 0, 12.5, 75, 100, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (28,0): 0, 0, 0, 25, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (29,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (30,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (31,0): 0, 0, 0, 12.5, 87.5, 100, 100, 87.5, 12.5, 0, 0, 0, 0, 0,
+         (32,0): 0, 0, 0, 12.5, 87.5, 100, 100, 75, 12.5, 0, 0, 0, 0, 0,
+         (33,0): 0, 0, 0, 12.5, 87.5, 100, 87.5, 25, 0, 0, 0, 0, 0, 0,
+         (34,0): 0, 0, 0, 12.5, 75, 100, 87.5, 12.5, 0, 0, 0, 0, 0, 0,
+         (35,0): 0, 0, 0, 0, 25, 87.5, 75, 12.5, 0, 0, 0, 0, 0, 0,
+         (36,0): 0, 0, 0, 0, 12.5, 62.5, 25, 0, 0, 0, 25, 0, 0, 0,
+         (37,0): 0, 0, 0, 0, 0, 12.5, 0, 0, 0, 25, 125, 25, 0, 0,
+         (38,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 25, 150, 50, 0, 0,
+         (39,0): 25, 0, 0, 0, 0, 0, 0, 0, 0, 25, 175, 150, 25, 0,
+         (40,0): 25, 0, 0, 0, 0, 0, 0, 0, 0, 50, 175, 175, 25, 0,
+         (41,0): 25, 0, 0, 0, 0, 0, 0, 0, 25, 150, 200, 175, 25, 0,
+         (42,0): 25, 0, 0, 0, 0, 0, 0, 0, 25, 175, 200, 175, 25, 0,
+         (43,0): 25, 0, 0, 0, 0, 0, 0, 0, 25, 175, 200, 175, 25, 0,
+         (44,0): 25, 0, 0, 0, 0, 0, 0, 0, 25, 150, 200, 175, 25, 0,
+         (45,0): 25, 0, 0, 0, 0, 0, 0, 0, 0, 50, 175, 175, 25, 0,
+         (46,0): 25, 0, 0, 0, 0, 0, 0, 0, 0, 25, 175, 150, 25, 0,
+         (47,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 25, 150, 50, 0, 0,
+         (48,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 25, 125, 25, 0, 0,
+         (49,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 25, 0, 0, 0,
+         (50,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (51,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (52,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (53,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (54,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (55,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (56,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (57,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (58,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (59,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (60,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (61,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
          }
       }
    }
@@ -89,88 +89,106 @@ GROUP "/" {
          DATATYPE  H5T_IEEE_F64LE
          DATASPACE  SIMPLE { ( 62, 14 ) / ( 62, 14 ) }
          DATA {
-         (0,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (1,0): 1e+06, 203125, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (2,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (3,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (4,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (5,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (6,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (7,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (8,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (9,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (10,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (11,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (12,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (13,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (14,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (15,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (16,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (17,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (18,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (19,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (20,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (21,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (22,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (23,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (24,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (25,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (26,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (27,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (28,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (29,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (30,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (31,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (32,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (33,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (34,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (35,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (36,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (37,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (38,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (39,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (40,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (41,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (42,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (43,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (44,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (45,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (46,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (47,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (48,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (49,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (50,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (51,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (52,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (53,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (54,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (55,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (56,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (57,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (58,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (59,0): 1e+06, 218750, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (60,0): 1e+06, 203125, 15625, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-         (61,0): 1e+06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+         (0,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (1,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (2,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (3,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (4,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (5,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (6,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (7,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (8,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (9,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (10,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (11,0): 0, 0, 0, 0, 0, 1.5625, 0, 0, 0, 0, 0, 0, 0, 0,
+         (12,0): 0, 0, 0, 0, 3.125, 14.0625, 4.6875, 0, 0, 0, 0, 0, 0, 0,
+         (13,0): 0, 0, 0, 1.5625, 17.1875, 48.4375, 29.6875, 4.6875, 0, 0, 0,
+         (13,11): 0, 0, 0,
+         (14,0): 0, 0, 0, 4.6875, 34.375, 76.5625, 64.0625, 17.1875, 1.5625,
+         (14,9): 0, 0, 0, 0, 0,
+         (15,0): 0, 0, 1.5625, 17.1875, 65.625, 93.75, 78.125, 21.875,
+         (15,8): 1.5625, 0, 0, 0, 0, 0,
+         (16,0): 0, 0, 1.5625, 20.3125, 78.125, 96.875, 82.8125, 34.375,
+         (16,8): 4.6875, 0, 0, 0, 0, 0,
+         (17,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 95.3125, 65.625,
+         (17,8): 17.1875, 1.5625, 0, 0, 0, 0,
+         (18,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 98.4375, 78.125,
+         (18,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (19,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 98.4375, 79.6875,
+         (19,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (20,0): 0, 0, 1.5625, 21.875, 79.6875, 98.4375, 98.4375, 79.6875,
+         (20,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (21,0): 0, 0, 4.6875, 34.375, 82.8125, 98.4375, 98.4375, 79.6875,
+         (21,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (22,0): 0, 1.5625, 17.1875, 65.625, 95.3125, 100, 98.4375, 79.6875,
+         (22,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (23,0): 0, 1.5625, 20.3125, 78.125, 98.4375, 100, 98.4375, 79.6875,
+         (23,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (24,0): 0, 1.5625, 20.3125, 79.6875, 98.4375, 100, 98.4375, 79.6875,
+         (24,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (25,0): 0, 1.5625, 20.3125, 79.6875, 98.4375, 100, 98.4375, 79.6875,
+         (25,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (26,0): 0, 1.5625, 20.3125, 78.125, 98.4375, 100, 98.4375, 79.6875,
+         (26,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (27,0): 0, 1.5625, 17.1875, 65.625, 95.3125, 100, 98.4375, 79.6875,
+         (27,8): 20.3125, 1.5625, 0, 0, 0, 1.5625,
+         (28,0): 0, 0, 4.6875, 34.375, 82.8125, 98.4375, 98.4375, 79.6875,
+         (28,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (29,0): 0, 0, 1.5625, 21.875, 79.6875, 98.4375, 98.4375, 79.6875,
+         (29,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (30,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 98.4375, 79.6875,
+         (30,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (31,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 98.4375, 78.125,
+         (31,8): 20.3125, 1.5625, 0, 0, 0, 0,
+         (32,0): 0, 0, 1.5625, 20.3125, 79.6875, 98.4375, 95.3125, 65.625,
+         (32,8): 17.1875, 1.5625, 0, 0, 0, 0,
+         (33,0): 0, 0, 1.5625, 20.3125, 78.125, 96.875, 82.8125, 34.375,
+         (33,8): 4.6875, 0, 0, 0, 0, 0,
+         (34,0): 0, 0, 1.5625, 17.1875, 65.625, 93.75, 78.125, 21.875,
+         (34,8): 1.5625, 0, 0, 0, 0, 0,
+         (35,0): 0, 0, 0, 4.6875, 34.375, 76.5625, 64.0625, 17.1875, 1.5625,
+         (35,9): 0, 3.125, 0, 0, 0,
+         (36,0): 0, 0, 0, 1.5625, 17.1875, 48.4375, 29.6875, 4.6875, 0, 6.25,
+         (36,10): 28.125, 6.25, 0, 0,
+         (37,0): 3.125, 0, 0, 0, 3.125, 14.0625, 4.6875, 0, 3.125, 31.25,
+         (37,10): 90.625, 34.375, 3.125, 0,
+         (38,0): 9.375, 0, 0, 0, 0, 1.5625, 0, 0, 3.125, 37.5, 121.875,
+         (38,11): 65.625, 9.375, 0,
+         (39,0): 34.375, 3.125, 0, 0, 0, 0, 0, 0, 3.125, 43.75, 150, 128.125,
+         (39,12): 34.375, 3.125,
+         (40,0): 40.625, 3.125, 0, 0, 0, 0, 0, 0, 9.375, 68.75, 162.5,
+         (40,11): 153.125, 40.625, 3.125,
+         (41,0): 40.625, 3.125, 0, 0, 0, 0, 0, 3.125, 34.375, 131.25, 187.5,
+         (41,11): 159.375, 40.625, 3.125,
+         (42,0): 40.625, 3.125, 0, 0, 0, 0, 0, 3.125, 40.625, 156.25, 193.75,
+         (42,11): 159.375, 40.625, 3.125,
+         (43,0): 40.625, 3.125, 0, 0, 0, 0, 0, 3.125, 40.625, 156.25, 193.75,
+         (43,11): 159.375, 40.625, 3.125,
+         (44,0): 40.625, 3.125, 0, 0, 0, 0, 0, 3.125, 34.375, 131.25, 187.5,
+         (44,11): 159.375, 40.625, 3.125,
+         (45,0): 40.625, 3.125, 0, 0, 0, 0, 0, 0, 9.375, 68.75, 162.5,
+         (45,11): 153.125, 40.625, 3.125,
+         (46,0): 34.375, 3.125, 0, 0, 0, 0, 0, 0, 3.125, 43.75, 150, 128.125,
+         (46,12): 34.375, 3.125,
+         (47,0): 9.375, 0, 0, 0, 0, 0, 0, 0, 3.125, 37.5, 121.875, 65.625,
+         (47,12): 9.375, 0,
+         (48,0): 3.125, 0, 0, 0, 0, 0, 0, 0, 3.125, 31.25, 90.625, 34.375,
+         (48,12): 3.125, 0,
+         (49,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 6.25, 28.125, 6.25, 0, 0,
+         (50,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3.125, 0, 0, 0,
+         (51,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (52,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (53,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (54,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (55,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (56,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (57,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (58,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (59,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (60,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+         (61,0): 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
          }
       }
    }
 }
 }
-HDF5 "ex5-meta0x0.h5" {
-GROUP "/" {
-   DATASET "dsize" {
-      DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
-      DATA {
-      (0): 62, 14
-      }
-   }
-   DATASET "psize" {
-      DATATYPE  H5T_STD_I32LE
-      DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
-      DATA {
-      (0): 1, 1
-      }
-   }
-}
-}
diff --git a/ex5.log b/ex5.log
index 1e0084b..6295c83 100644
--- a/ex5.log
+++ b/ex5.log
@@ -1,15 +1,46 @@
 [PDI][Trace-plugin] *** info: Welcome!
 [PDI][Trace-plugin] *** info: !!!                            named event: initialization
-[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
-[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: pcoord
 [PDI][Trace-plugin] *** info: <<= data stop being available in the store: pcoord
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: dsize
 [PDI][Trace-plugin] *** info: <<= data stop being available in the store: dsize
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: psize
 [PDI][Trace-plugin] *** info: <<= data stop being available in the store: psize
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
 [PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
+[PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
+[PDI][Trace-plugin] *** info: !!!                            named event: loop
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: main_field
+[PDI][Trace-plugin] *** info: <<= data stop being available in the store: ii
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: ii
 [PDI][Trace-plugin] *** info: =>>   data becoming available in the store: main_field
 [PDI][Trace-plugin] *** info: !!!                            named event: loop
diff --git a/ex5.yml b/ex5.yml
index d9d28b5..ae516aa 100644
--- a/ex5.yml
+++ b/ex5.yml
@@ -17,13 +17,19 @@ pdi:
     trace:
       logging: { pattern: '[PDI][%n-plugin] *** %l: %v' }
     decl_hdf5:
-      - file: ex5-meta${pcoord[0]}x${pcoord[1]}.h5
+      - file: ex5-meta-${pcoord[0]}x${pcoord[1]}.h5
         write: [ dsize, psize ]
-      - file: ex5-data${pcoord[0]}x${pcoord[1]}.h5
-        on_event: ""
-        when: '$ii>0 & ' # `&' is a local `and' operation
+      - file: ex5-data-${pcoord[0]}x${pcoord[1]}.h5
+        #*** enable the output upon the event
+        #...
+        #*** enable the output when ii>0 and ii<3 (`&` is a logical `and` operation )
+        #...
         write:
           ii: # name of the PDI data to write
-            dataset: 'iter${}/ii' # dataset name in file, $-expressions can be used here, "/" separate groups in path
+            #*** give the dataset that you want to write into for ii
+            # $-expressions can be used to define dataset name in file, , "/" separate groups in path
+            #...
           main_field:
-            dataset: 'iter${}/main_field'
+            #*** give the dataset that you want to write into for main_field
+            # $-expressions can be used to define dataset name in file, , "/" separate groups in path
+            #...
diff --git a/solutions/ex3.yml b/solutions/ex3.yml
index e80547e..e5d3fe8 100644
--- a/solutions/ex3.yml
+++ b/solutions/ex3.yml
@@ -6,12 +6,15 @@ global_size: { height: 60, width: 12 }
 parallelism: { height: 1, width: 1 }
 # PDI configuration
 pdi:
+  #*** describe the data dsize, psize, pcoord
   data:
-    ii: int
     dsize: { type: array, subtype: int, size: 2 }
     psize: { type: array, subtype: int, size: 2 }
     pcoord: { type: array, subtype: int, size: 2 }
+  
   plugins:
+    trace:
     decl_hdf5:
+    #*** use the decl_hdf5 plugin to write in the file ex3.h5 the data above (dsize, psize, pcoord)
       file: ex3.h5
       write: [ dsize, psize, pcoord ]
diff --git a/solutions/ex4.yml b/solutions/ex4.yml
index 5536b7a..3d3704b 100644
--- a/solutions/ex4.yml
+++ b/solutions/ex4.yml
@@ -3,20 +3,24 @@ alpha: 0.125
 # global data-size (excluding spacer for boundary conditions or ghosts)
 global_size: { height: 60, width: 12 }
 # degree of parallelism (number of blocks in each dimension)
-parallelism: { height: 2 , width: 1 }
+parallelism: { height: 2 , width: 2 }
 # PDI configuration
 pdi:
   metadata: # small values for which PDI keeps a copy
+    #*** add ii as metadata
     ii: int
     dsize: { type: array, subtype: int, size: 2 }
     psize: { type: array, subtype: int, size: 2 }
     pcoord: { type: array, subtype: int, size: 2 }
   data: # values for which PDI does not keep a copy
-    main_field: { type: array, subtype: double, size: [ '$dsize[0]', '$dsize[1]' ] } # we can use $ expressions in type definitions
+    #*** add main_field to the data section, use $-expression to define its size
+    main_field: { type: array, subtype: double, size: [ '$dsize[0]', '$dsize[1]' ] } 
   plugins:
     decl_hdf5:
-      - file: ex4-meta${pcoord[0]}x${pcoord[1]}.h5  # we can use $ expressions in file names
+      #*** write dsize and psize into hdf5, one file per rank
+      - file: ex4-metadata-${pcoord[0]}x${pcoord[1]}.h5  # we can use $ expressions in file names
         write: [ dsize, psize ]
-      - file: ex4-data${pcoord[0]}x${pcoord[1]}.h5
-        when: '$ii=1'  # we can use $ expressions in conditions
-        write: [ ii, main_field ]
+      #*** write main_field and iteration counter into hdf5, one file per rank at first iteration (ii=1)
+      - file: ex4-data-${pcoord[0]}x${pcoord[1]}_iter_${ii}.h5
+        when: '$ii=1'
+        write: [ii,  main_field ]
diff --git a/solutions/ex5.c b/solutions/ex5.c
index fc95d84..df43264 100644
--- a/solutions/ex5.c
+++ b/solutions/ex5.c
@@ -44,13 +44,32 @@ int pcoord[2];
 /// the alpha coefficient used in the computation
 double alpha;
 
+double L=1.0;
+double source1[4]={0.4, 0.4, 0.2, 100};
+double source2[4]={0.7, 0.8, 0.1, 200};
+
 /** Initialize the data all to 0 except for the left border (XX==0) initialized to 1 million
  * \param[out] dat the local data to initialize
  */
 void init(double dat[dsize[0]][dsize[1]])
 {
 	for (int yy=0; yy<dsize[0]; ++yy)  for (int xx=0; xx<dsize[1]; ++xx)  dat[yy][xx] = 0;
-	if ( pcoord[1] == 0 ) for (int yy=0; yy<dsize[0]; ++yy)  dat[yy][0] = 1000000;
+	double dy = L / ((dsize[0]-2) *psize[0]) ;
+	double dx = L / ((dsize[1]-2) *psize[1]) ;
+
+	double cpos_x,cpos_y;
+	for(int yy=0; yy<dsize[0];++yy) {
+		cpos_y=(yy+pcoord[0]*(dsize[0]-2))*dy-0.5*dy;
+		for(int xx=0; xx<dsize[1];++xx) {
+			cpos_x=(xx+pcoord[1]*(dsize[1]-2))*dx-0.5*dx;
+			if((cpos_y-source1[0])*(cpos_y-source1[0]) + (cpos_x-source1[1])*(cpos_x-source1[1]) <= source1[2]*source1[2]) {
+				dat[yy][xx] = source1[3];
+			}
+			if((cpos_y-source2[0])*(cpos_y-source2[0]) + (cpos_x-source2[1])*(cpos_x-source2[1]) <= source2[2]*source2[2]) {
+				dat[yy][xx] = source2[3];
+			}
+		}
+	}
 }
 
 /** Compute the values at the next time-step based on the values at the current time-step
@@ -60,21 +79,15 @@ void init(double dat[dsize[0]][dsize[1]])
 void iter(double cur[dsize[0]][dsize[1]], double next[dsize[0]][dsize[1]])
 {
 	int xx, yy;
-	for (xx=0; xx<dsize[1]; ++xx) next[0][xx] = cur[0][xx];
 	for (yy=1; yy<dsize[0]-1; ++yy) {
-		next[yy][0] = cur[yy][0];
 		for (xx=1; xx<dsize[1]-1; ++xx) {
-			next[yy][xx] =
-					  (1.-4.*alpha) * cur[yy][xx]
-					+        alpha  * (   cur[yy][xx-1]
-					                    + cur[yy][xx+1]
-					                    + cur[yy-1][xx]
-					                    + cur[yy+1][xx]
-					                  ); 
+			next[yy][xx] = (1.-4.*alpha) * cur[yy][xx]
+					             +alpha  * ( cur[yy][xx-1]
+					                       + cur[yy][xx+1]
+					                       + cur[yy-1][xx]
+					                       + cur[yy+1][xx]); 
 		}
-		next[yy][dsize[1]-1] = cur[yy][dsize[1]-1];
 	}
-	for (xx=0; xx<dsize[1]; ++xx) next[dsize[0]-1][xx] = cur[dsize[0]-1][xx];
 }
 
 /** Exchanges ghost values with neighbours
@@ -104,8 +117,8 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send up
 	MPI_Cart_shift(cart_comm, 0, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send column after ghost
-	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last column (ghost)
+	MPI_Sendrecv(&cur[1][1],          1, row, rank_dest,   100, // send row after ghost
+	             &cur[dsize[0]-1][1], 1, row, rank_source, 100, // receive last row (ghost)
 	             cart_comm, &status);
 	
 	// send to the right
@@ -116,7 +129,7 @@ void exchange(MPI_Comm cart_comm, double cur[dsize[0]][dsize[1]])
 	
 	// send to the left
 	MPI_Cart_shift(cart_comm, 1, -1, &rank_source, &rank_dest);
-	MPI_Sendrecv(&cur[1][1], 1, column, rank_dest,   100, // send column after ghost
+	MPI_Sendrecv(&cur[1][1],          1, column, rank_dest,   100, // send column after ghost
 	             &cur[1][dsize[1]-1], 1, column, rank_source, 100, // receive last column (ghost)
 	             cart_comm, &status);
 }
@@ -162,7 +175,7 @@ int main( int argc, char* argv[] )
 	dsize[1] = global_size[1]/psize[1] + 2;
 	
 	// create a 2D Cartesian MPI communicator & get our coordinate (rank) in it
-	int cart_period[2] = { 0, 0 };
+	int cart_period[2] = { 1, 1 };
 	MPI_Comm cart_comm; MPI_Cart_create(main_comm, 2, psize, cart_period, 1, &cart_comm);
 	MPI_Cart_coords(cart_comm, pcoord_1d, 2, pcoord);
 	
@@ -178,22 +191,20 @@ int main( int argc, char* argv[] )
 	int ii=0;
 	
 	// share useful configuration bits with PDI
-	PDI_share("ii",         &ii,    PDI_OUT);
-	PDI_reclaim("ii");
 	PDI_share("pcoord",     pcoord, PDI_OUT);
 	PDI_reclaim("pcoord");
 	PDI_share("dsize",      dsize,  PDI_OUT);
 	PDI_reclaim("dsize");
 	PDI_share("psize",      psize,  PDI_OUT);
 	PDI_reclaim("psize");
-	PDI_share("main_field", cur,    PDI_OUT);
-	PDI_reclaim("main_field");
+
 	
 	// the main loop
-	for (; ii<3; ++ii) {
+	for (; ii<4; ++ii) {
 		// share the loop counter & main field at each iteration
 		PDI_share("ii",         &ii, PDI_OUT);
 		PDI_share("main_field", cur, PDI_OUT);
+		//*** use PDI_event to prevent redundant open/close of the output file
 		PDI_event("loop");
 		PDI_reclaim("main_field");
 		PDI_reclaim("ii");
@@ -207,9 +218,8 @@ int main( int argc, char* argv[] )
 		// swap the current and next values
 		double (*tmp)[dsize[1]] = cur; cur = next; next = tmp;
 	}
-	// finally share the main field after the main loop body
+	// finally share the loop counter and main field after the main loop body
 	PDI_share("main_field", cur, PDI_OUT);
-	// as well as the loop counter
 	PDI_share("ii",         &ii, PDI_OUT);
 	PDI_reclaim("ii");
 	PDI_reclaim("main_field");
diff --git a/solutions/ex5.yml b/solutions/ex5.yml
index ae83504..f115752 100644
--- a/solutions/ex5.yml
+++ b/solutions/ex5.yml
@@ -17,13 +17,19 @@ pdi:
     trace:
       logging: { pattern: '[PDI][%n-plugin] *** %l: %v' }
     decl_hdf5:
-      - file: ex5-meta${pcoord[0]}x${pcoord[1]}.h5
+      - file: ex5-meta-${pcoord[0]}x${pcoord[1]}.h5
         write: [ dsize, psize ]
-      - file: ex5-data${pcoord[0]}x${pcoord[1]}.h5
+      - file: ex5-data-${pcoord[0]}x${pcoord[1]}.h5
+        #*** enable the output upon the event
         on_event: loop
-        when: '$ii>0 & $ii<3' # `&' is a logical `and' operation
+        #*** enable the output when ii>0 and ii<3 (`&` is a logical `and` operation )
+        when: '$ii>0 & $ii<3' 
         write:
           ii: # name of the PDI data to write
-            dataset: 'iter${ii}/ii' # dataset name in file, $-expressions can be used here, "/" separate groups in path
+            #*** give the dataset that you want to write into for ii
+            # $-expressions can be used to define dataset name in file, , "/" separate groups in path
+            dataset: 'iter${ii}/ii' 
           main_field:
+            #*** give the dataset that you want to write into for main_field
+            # $-expressions can be used to define dataset name in file, , "/" separate groups in path
             dataset: 'iter${ii}/main_field'