diff --git a/README.rst b/README.rst
index 6193f18..0eab496 100644
--- a/README.rst
+++ b/README.rst
@@ -20,7 +20,7 @@ A **G**\ enetic **A**\ lgorithm **F**\ ramework in py\ **T**\ hon
     :target: https://www.python.org/downloads/release/python-351/
     :alt: platform
 
-.. image:: https://img.shields.io/badge/pypi-v0.5.4-blue.svg
+.. image:: https://img.shields.io/badge/pypi-v0.6.0-blue.svg
     :target: https://pypi.python.org/pypi/gaft/
     :alt: versions
 
diff --git a/gaft/__init__.py b/gaft/__init__.py
index 8c74bfc..78aabb6 100644
--- a/gaft/__init__.py
+++ b/gaft/__init__.py
@@ -3,7 +3,7 @@
 
 from .engine import GAEngine
 
-__version__ = '0.5.4'
+__version__ = '0.6.0'
 __author__ = 'ShaoZhengjiang <shaozhengjiang@gmail.com>'
 
 # Set root logger.
diff --git a/gaft/components/binary_individual.py b/gaft/components/binary_individual.py
index e9f1853..c9a68a1 100644
--- a/gaft/components/binary_individual.py
+++ b/gaft/components/binary_individual.py
@@ -8,7 +8,9 @@
 import logging
 
 from .individual import IndividualBase
-from ..mpiutil import mpi
+from ..mpiutil import MPIUtil
+
+mpi = MPIUtil()
 
 
 class BinaryIndividual(IndividualBase):
diff --git a/gaft/engine.py b/gaft/engine.py
index 6b1f443..f7f8278 100644
--- a/gaft/engine.py
+++ b/gaft/engine.py
@@ -1,7 +1,8 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-''' Genetic Algorithm engine definition '''
+''' Genetic Algorithm engine definition
+'''
 
 import logging
 import math
@@ -15,8 +16,9 @@
 from .components import IndividualBase, Population
 from .plugin_interfaces.operators import Selection, Crossover, Mutation
 from .plugin_interfaces.analysis import OnTheFlyAnalysis
-from .mpiutil import mpi
+from .mpiutil import MPIUtil
 
+mpi = MPIUtil()
 
 def do_profile(filename, sortby='tottime'):
     ''' Constructor for function profiling decorator.
@@ -84,7 +86,29 @@ def __set__(self, engine, value):
 
 
 class GAEngine(object):
-    ''' Class for representing a Genetic Algorithm engine.
+    ''' Class for representing a Genetic Algorithm engine. The class is the 
+    central object in GAFT framework for running a genetic algorithm optimization.
+    Once the population with individuals,  a set of genetic operators and fitness 
+    function are setup, the engine object unites these informations and provide 
+    means for running a genetic algorthm optimization.
+
+    :param population: The Population to be reproduced in evolution iteration.
+    :type population: :obj:`gaft.components.Population`
+
+    :param selection: The Selection to be used for individual seleciton.
+    :type selection: :obj:`gaft.plugin_interfaces.operators.Selection`
+
+    :param crossover: The Crossover to be used for individual crossover.
+    :type crossover: :obj:`gaft.plugin_interfaces.operators.Crossover`
+
+    :param mutation: The Mutation to be used for individual mutation.
+    :type mutation: :obj:`gaft.plugin_interfaces.operators.Mutation`
+
+    :param fitness: The fitness calculation function for an individual in population.
+    :type fitness: function
+
+    :param analysis: All analysis class for on-the-fly analysis.
+    :type analysis: :obj:`OnTheFlyAnalysis` list
     '''
     # Statistical attributes for population.
     fmax, fmin, fmean = StatVar('fmax'), StatVar('fmin'), StatVar('fmean')
@@ -94,30 +118,6 @@ class GAEngine(object):
 
     def __init__(self, population, selection, crossover, mutation,
                  fitness=None, analysis=None):
-        ''' Genetic algorithm engine. The class is the central object in GAFT framework
-        for running a genetic algorithm optimization. Once the population with
-        individuals,  a set of genetic operators and fitness function are setup,
-        the engine object unites these informations and provide means for running
-        a genetic algorthm optimization.
-
-        :param population: The Population to be reproduced in evolution iteration.
-        :type population: :obj:`gaft.components.Population`
-
-        :param selection: The Selection to be used for individual seleciton.
-        :type selection: :obj:`gaft.plugin_interfaces.operators.Selection`
-
-        :param crossover: The Crossover to be used for individual crossover.
-        :type crossover: :obj:`gaft.plugin_interfaces.operators.Crossover`
-
-        :param mutation: The Mutation to be used for individual mutation.
-        :type mutation: :obj:`gaft.plugin_interfaces.operators.Mutation`
-
-        :param fitness: The fitness calculation function for an individual in population.
-        :type fitness: function
-
-        :param analysis: All analysis class for on-the-fly analysis.
-        :type analysis: :obj:`OnTheFlyAnalysis` list
-        '''
         # Set logger.
         logger_name = 'gaft.{}'.format(self.__class__.__name__)
         self.logger = logging.getLogger(logger_name)
@@ -303,10 +303,12 @@ def linear_scaling(self, target='max', ksi=0.5):
         :param ksi: Selective pressure adjustment value.
         :type ksi: float
 
-        Note::
+        .. Note::
+
             Linear Scaling:
-                1. arg max f(x), then f' = f - min{f(x)} + ksi;
-                2. arg min f(x), then f' = max{f(x)} - f(x) + ksi;
+                1. :math:`arg \max f(x)`, then the scaled fitness would be :math:`f - \min f(x) + {\\xi}`
+                2. :math:`arg \min f(x)`, then the scaled fitness would be :math:`\max f(x) - f(x) + {\\xi}`
+
         '''
         def _linear_scaling(fn):
             # For original fitness calculation.
@@ -346,9 +348,10 @@ def dynamic_linear_scaling(self, target='max', ksi0=2, r=0.9):
                   value is 0.9
         :type r: float in range [0.9, 0.999]
 
-        Note::
+        .. Note::
             Dynamic Linear Scaling:
-            For maximizaiton, f' = f(x) - min{f(x)} + ksi^k, k is generation number.
+
+            For maximizaiton, :math:`f' = f(x) - \min f(x) + {\\xi}^{k}`, :math:`k` is generation number.
         '''
         def _dynamic_linear_scaling(fn):
             # For original fitness calculation.
diff --git a/gaft/mpiutil.py b/gaft/mpiutil.py
index 7837ceb..f7a221d 100644
--- a/gaft/mpiutil.py
+++ b/gaft/mpiutil.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 '''
-Utitlities for parallelizing Genetic Algorithm by using MPI interfaces
+A high-level utility class for parallelizing Genetic Algorithm by using MPI interfaces
 in distributed MPI environment.
 '''
 
@@ -16,12 +16,30 @@
     MPI_INSTALLED = False
 
 
+class Singleton(type):
+    def __call__(cls, *args, **kwargs):
+        if not hasattr(cls, '_instance'):
+            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
+        return cls._instance
+
+
 class MPIUtil(object):
+
+    __metaclass__ = Singleton
+
     def __init__(self):
+        ''' Wrapper class for higher level of MPI interfaces that will create a
+        singleton for parallelization.
+        '''
         logger_name = 'gaft.{}'.format(self.__class__.__name__)
         self._logger = logging.getLogger(logger_name)
 
     def bcast(self, data):
+        ''' Broadcast data to MPI processes
+
+        :param data: Data to be broadcasted
+        :type data: any Python object
+        '''
         if MPI_INSTALLED:
             mpi_comm = MPI.COMM_WORLD
             bdata = mpi_comm.bcast(data, root=0)
@@ -31,12 +49,16 @@ def bcast(self, data):
 
     # Wrapper for common MPI interfaces.
     def barrier(self):
+        ''' Block until all processes in the communicator have reached this routine
+        '''
         if MPI_INSTALLED:
             mpi_comm = MPI.COMM_WORLD
             mpi_comm.barrier()
 
     @property
     def rank(self):
+        ''' Get the rank of the calling process in the communicator
+        '''
         if MPI_INSTALLED:
             mpi_comm = MPI.COMM_WORLD
             return mpi_comm.Get_rank()
@@ -45,6 +67,8 @@ def rank(self):
 
     @property
     def size(self):
+        ''' Get the size of the group associated with a communicator
+        '''
         if MPI_INSTALLED:
             mpi_comm = MPI.COMM_WORLD
             return mpi_comm.Get_size()
@@ -53,12 +77,19 @@ def size(self):
 
     @property
     def is_master(self):
+        ''' If current process is the master process
+        '''
         return self.rank == 0
 
     # Utility methods.
     def split_seq(self, sequence):
-        '''
-        Split the sequence according to rank and processor number.
+        ''' Split the sequence according to rank and processor number.
+
+        :param sequence: Data sequence to be splitted
+        :type sequence: any Python object list
+
+        :return: Sub data sequence for current process
+        :rtype: any Python object list
         '''
         starts = [i for i in range(0, len(sequence), len(sequence)//self.size)]
         ends = starts[1: ] + [len(sequence)]
@@ -67,8 +98,13 @@ def split_seq(self, sequence):
         return sequence[start: end]
 
     def split_size(self, size):
-        '''
-        Split a size number(int) to sub-size number.
+        ''' Split a size number(int) to sub-size number.
+
+        :param size: The size number to be splitted.
+        :type size: int
+
+        :return: Sub-size for current process
+        :rtype: int
         '''
         if size < self.size:
             warn_msg = ('Splitting size({}) is smaller than process ' +
@@ -87,8 +123,13 @@ def split_size(self, size):
         return splited_sizes[self.rank]
 
     def merge_seq(self, seq):
-        '''
-        Gather data in sub-process to root process.
+        ''' Gather data in sub-process to root process.
+
+        :param seq: Sub data sequence for current process
+        :type seq: any Python object list
+
+        :return: Merged data sequence from all processes in a communicator
+        :rtype: any Python object list
         '''
         if self.size == 1:
             return seq
@@ -98,13 +139,8 @@ def merge_seq(self, seq):
         return list(chain(*merged_seq))
 
 
-mpi = MPIUtil()
-
-
 def master_only(func):
-    '''
-    Decorator to limit a function to be called
-    only in master process in MPI env.
+    ''' Decorator to limit a function to be called only in master process in MPI env.
     '''
     @wraps(func)
     def _call_in_master_proc(*args, **kwargs):
diff --git a/gaft/operators/mutation/flip_bit_mutation.py b/gaft/operators/mutation/flip_bit_mutation.py
index 8d7195b..c29468f 100644
--- a/gaft/operators/mutation/flip_bit_mutation.py
+++ b/gaft/operators/mutation/flip_bit_mutation.py
@@ -5,11 +5,13 @@
 
 from random import random, uniform
 
-from ...mpiutil import mpi
+from ...mpiutil import MPIUtil
 from ...plugin_interfaces.operators.mutation import Mutation
 from ...components.binary_individual import BinaryIndividual
 from ...components.decimal_individual import DecimalIndividual
 
+mpi = MPIUtil()
+
 
 class FlipBitMutation(Mutation):
     def __init__(self, pm):
diff --git a/setup.py b/setup.py
index 49de297..963e534 100644
--- a/setup.py
+++ b/setup.py
@@ -31,7 +31,7 @@
     :target: https://www.python.org/downloads/release/python-351/
     :alt: platform
 
-.. image:: https://img.shields.io/badge/pypi-v0.5.4-blue.svg
+.. image:: https://img.shields.io/badge/pypi-v0.6.0-blue.svg
     :target: https://pypi.python.org/pypi/gaft/
     :alt: versions
 
diff --git a/tests/mpiutil_test.py b/tests/mpiutil_test.py
index b421a7c..8c6a401 100644
--- a/tests/mpiutil_test.py
+++ b/tests/mpiutil_test.py
@@ -6,7 +6,9 @@
 
 import unittest
 
-from gaft.mpiutil import mpi
+from gaft.mpiutil import MPIUtil
+
+mpi = MPIUtil()
 
 
 class MPIUtilTest(unittest.TestCase):