old_contents: class VolumeFunctionTime(object):
      def __init__(self):
          """
          The init function should be used to import any parameters
          for the volume as a function of time from external files
          """
          pass
      def __call__(self,time):
          """
          The call function should be where the implementation of the
          volume as a function of time is done.
          """
          return 0
      
  class TemperatureFunctionTime(object):
      def __init__(self):
          """
          The init function should be used to import any parameters
          for the temperature as a function of time from external files
          """ 
          pass
      def __call__(self,time):
          """
          The call function should be where the implementation of the
          temperature as a function of time is done.
          """
          return None
      def run_simulation(self):
          """
          This method actually runs the simulation. For now it is a dummy
          method, pending a decision about how to run the simulation. May
          be deleted at any point.
          """
          pass
      
new_contents: class VolumeFunctionTime(object):
      """
      Calculate the volume of the reactor as a user specified function 
      of time.
      """
      def __init__(self):
          """Set up the function to be calculated.
          
          The init function should be used to import any parameters for 
          the volume as a function of time from external files. Do not
          calculate the volume as a function of time here. Store all of
          the parameters in the ``self`` instance. The reason for this is 
          to avoid running the ``__init__`` function on every time step.
          See the example below.
          
          Example to load polynomial parameters from a file:
          
              # Read the file into the list ``self.params``. The lines of 
              # the file are read as strings.
              with open('file.txt','r') as input_file:
                  self.params = input_file.readlines()
              # Convert the strings to floats.
              self.params = [float(param) for param in self.params]
              self.area = 1 # m**2
          """
          pass
          
      def __call__(self,time):
          """Return the velocity of the piston at the given time.
          
          The call function should be where the implementation of the
          volume as a function of time is done. Cantera expects the 
          velocity to be returned - v = dV/dt * 1/A. Get all of the
          needed parameters that were stored in the ``self`` instance.
          See the example below.
          
          Example to use the previously stored polynomial parameters:
          
              volume = (self.params[0] + self.params[1]*time + 
                  self.params[2]*time**2 + self.params[3]*time**3) # m**3
              dvoldt = (self.params[1] + 2*self.params[2]*time + 
                  3*self.params[3]*time**2) # m**3/s
              velocity = dvoldt/self.area # m/s
              return velocity 
          """
          return 0
      
  class TemperatureFunctionTime(object):
      """
      Calculate the temperature of the reactor as a user specified 
      function of time.
      """
      def __init__(self):
          """Set up the function to be calculated.
          
          The init function should be used to import any parameters for 
          the temperature as a function of time from external files. Do not
          calculate the temperature as a function of time here. Store all of
          the parameters in the ``self`` instance. The reason for this is 
          to avoid running the ``__init__`` function on every time step.
          See the example below.
          
          Example to load polynomial parameters from a file:
          
              # Read the file into the list ``self.params``. The lines of 
              # the file are read as strings.
              with open('file.txt','r') as input_file:
                  self.params = input_file.readlines()
              # Convert the strings to floats.
              self.params = [float(param) for param in self.params]
          """
          pass
          
      def __call__(self,time):
          """Return the velocity of the piston at the given time.
          
          The call function should be where the implementation of the
          temperature as a function of time is done. Get all of the
          needed parameters that were stored in the ``self`` instance.
          See the example below. Note: ``None`` is not a valid return
          value, so this function does not work as written.
          
          Example to use the previously stored polynomial parameters:
          
              temperature = (self.params[0] + self.params[1]*time + 
                  self.params[2]*time**2 + self.params[3]*time**3) # K
              return temperature 
          """
          return None
          
subject: Add docs to user_routines. Work on #9