diff --git a/source/pysph/sph/funcs/arithmetic_funcs.pyx b/source/pysph/sph/funcs/arithmetic_funcs.pyx
index 8cf7a4f..d24a0ec 100644
--- a/source/pysph/sph/funcs/arithmetic_funcs.pyx
+++ b/source/pysph/sph/funcs/arithmetic_funcs.pyx
@@ -13,7 +13,7 @@ cdef class PropertyGet(SPHFunction):
         dest -- The destination particle array
         prop_names -- The properties to get (upto 3 particle arrays)
         """
-        self.prop_names = prop_names
+        self.prop_names = list(prop_names)
         SPHFunction.__init__(self, source, dest, setup_arrays=True)
         self.num_outputs = len(prop_names)
         self.id = 'property_get'
@@ -47,7 +47,7 @@ cdef class PropertyAdd(SPHFunction):
         prop_names -- The properties to get the sum of
         constant -- a constant value to add to the result
         """
-        self.prop_names = prop_names
+        self.prop_names = list(prop_names)
         self.constant = constant
         SPHFunction.__init__(self, source, dest, setup_arrays=True)
         self.num_outputs = 1
@@ -83,7 +83,7 @@ cdef class PropertyNeg(SPHFunction):
         dest -- The destination particle array.
         prop_names -- The properties to get the inverse of (upto 3)
         """
-        self.prop_names = prop_names
+        self.prop_names = list(prop_names)
         SPHFunction.__init__(self, source, dest, setup_arrays=True)
         self.num_outputs = len(prop_names)
         self.id = 'property_neg'
@@ -117,7 +117,7 @@ cdef class PropertyMul(SPHFunction):
         prop_names -- The properties to get product of
         constant -- a constant value to multiply to the result
         """
-        self.prop_names = prop_names
+        self.prop_names = list(prop_names)
         self.constant = constant
         SPHFunction.__init__(self, source, dest, setup_arrays=True)
         self.num_outputs = 1
@@ -153,7 +153,7 @@ cdef class PropertyInv(SPHFunction):
         dest -- The destination particle array.
         prop_names -- The properties to get inverse of (upto 3)
         """
-        self.prop_names = prop_names
+        self.prop_names = list(prop_names)
         SPHFunction.__init__(self, source, dest, setup_arrays=True)
         self.num_outputs = len(prop_names)
         self.id = 'property_inv'
diff --git a/source/pysph/sph/sph_calc.pyx b/source/pysph/sph/sph_calc.pyx
index 7de97f3..d1bb79c 100644
--- a/source/pysph/sph/sph_calc.pyx
+++ b/source/pysph/sph/sph_calc.pyx
@@ -171,10 +171,11 @@ cdef class SPHCalc:
                 msg = 'SPHFunction.source not same as'
                 msg += ' SPHCalc.sources[%d]'%(i)
                 raise ValueError, msg
-            if funcs[i].num_outputs > len(self.updates):
-                raise ValueError, ('Number of updates not same as num_outputs'
-                       '; required %d, got %d %s for func %s'%(funcs[i].num_outputs,
-                                       len(self.updates), self.updates, funcs[i]))
+            if funcs[i].num_outputs != len(self.updates):
+                logger.warn('Number of updates not same as num_outputs; '
+                            'required %d, got %d %s for func %s'%(
+                                funcs[i].num_outputs, len(self.updates),
+                                self.updates, funcs[i]))
             # not valid for SPHFunction
             #if funcs[i].dest != self.dest:
             #    msg = 'SPHFunction.dest not same as'
@@ -216,6 +217,9 @@ cdef class SPHCalc:
 
         func = self.funcs[0]
 
+        # Add temporary array in case of fewer arguments to sph()
+        self.dest.add_property(dict(name='_tmp'))
+
         self.src_reads = func.src_reads
         self.dst_reads = func.dst_reads
 
@@ -223,17 +227,24 @@ cdef class SPHCalc:
               str output_array3=None, bint exclude_self=False): 
         """
         """
-        if output_array1 is None: output_array1 = '_tmpx'
-        if output_array2 is None: output_array2 = '_tmpy'
-        if output_array3 is None: output_array3 = '_tmpz'
-
-        cdef DoubleArray output1 = self.dest.get_carray(output_array1)
-        cdef DoubleArray output2 = self.dest.get_carray(output_array2)
-        cdef DoubleArray output3 = self.dest.get_carray(output_array3)
-        
-        if output1 is not None: self.reset_output_array(output1)
-        if output2 is not None: self.reset_output_array(output2)
-        if output3 is not None: self.reset_output_array(output3)
+        cdef DoubleArray output1, output2, output3
+        if output_array1 is None:
+            output1 = self.dest.get_carray('_tmp')
+        else:
+            output1 = self.dest.get_carray(output_array1)
+            self.reset_output_array(output1)
+
+        if output_array2 is None:
+            output2 = self.dest.get_carray('_tmp')
+        else:
+            output2 = self.dest.get_carray(output_array2)
+            self.reset_output_array(output2)
+
+        if output_array3 is None:
+            output3 = self.dest.get_carray('_tmp')
+        else:
+            output3 = self.dest.get_carray(output_array3)
+            self.reset_output_array(output3)
 
         self.sph_array(output1, output2, output3, exclude_self)
 
diff --git a/source/pysph/sph/tests/test_boundary_funcs.py b/source/pysph/sph/tests/test_boundary_funcs.py
index 3d4131a..4c71841 100644
--- a/source/pysph/sph/tests/test_boundary_funcs.py
+++ b/source/pysph/sph/tests/test_boundary_funcs.py
@@ -55,7 +55,7 @@ def setUp(self):
         rhof = numpy.ones_like(xf)
 
         self.fluid = base.get_particle_array(x=xf, y=yf, h=hf, m=mf, rho=rhof,
-                                             cs=cs, tmpx=mf, tmpy=mf, tmpz=mf,
+                                             cs=cs, ax=mf, ay=mf, az=mf,
                                              name='fluid', type=Fluid)
 
 
@@ -113,7 +113,7 @@ def test_force(self):
 
         self.particles.update()
 
-        calc.sph('tmpx', 'tmpy', 'tmpz')
+        calc.sph('ax', 'ay', 'az')
 
         force = fluid.tmpy