Linear Expression Module
========================

This class implements linear expressions.

    .. py:method:: coefficient(self, symbol)
        
        Return the coefficient value of the given symbol.
        
    .. py:method:: coefficients(self)
        
        Return a list of the coefficients of an expression
        
    .. py:method:: constant(self)
    
        Return the constant value of an expression.
        
    .. py:method:: symbols(self)
    
        Return a list of symbols in an expression.                            
    
    .. py:method:: dimension(self)
    
        Return the number of vriables in an expression.
        
    .. py:method:: __sub__(self, other)
    
        Return the difference between two expressions.
               
    .. py:method:: subs(self, symbol, expression=None)
    
        Subsitute the given value into an expression and return the resulting expression.

    .. py:method:: fromsympy(self)
    
        Convert sympy object to an expression.
        
    .. py:method:: tosympy(self)
    
        Return an expression as a sympy object.    
          
.. py:class:: Dummy(Symbol)

This class returns a dummy symbol to ensure that each no variables are repeated in an expression