old_contents: """A model of temperature diffusion over a rectangular plate."""
  import numpy as np
  import yaml
  
  
  class Diffusion(object):
      """Model of temperature diffusion on a plate."""
  
      def __init__(self, config_file=None):
          """Initialize the model."""
  
          if config_file is not None:
              with open(config_file, 'r') as fp:
                  parameters = yaml.load(fp)
              for key, value in parameters.items():
                  setattr(self, key, value)
          else:
              self.nx = 10
              self.ny = 10
              self.dx = 1.0
              self.dy = 1.0
              self.alpha = 0.9
  
          self.time = 0.0
          self.dt = min(self.dx, self.dy) ** 2.0 / (4.0 * self.alpha)
          self.dt /= 2.0
  
          self.temperature = np.zeros((self.ny, self.nx))
          self.new_temperature = self.temperature.copy()
  
      def advance(self):
          """Advance the model by one time step."""
  
          self.solve()
          self.time += self.dt
  
      def solve(self):
          """Solve the diffusion equation."""
  
          dx2, dy2 = self.dx**2, self.dy**2
          coef = self.alpha * self.dt / (2.0*(dx2 + dy2))
  
          for j in range(1, self.ny-1):
              for i in range(1, self.nx-1):
                  self.new_temperature[i,j] = \
                      self.temperature[i,j] + coef * (
                      dx2*(self.temperature[i,j-1] + self.temperature[i,j+1]) +
                      dy2*(self.temperature[i-1,j] + self.temperature[i+1,j]) -
                      2.0*(dx2 + dy2)*self.temperature[i,j])
  
          self.new_temperature[(0, -1), :] = 0.0
          self.new_temperature[:, (0, -1)] = 0.0
  
          self.temperature[:] = self.new_temperature
  
new_contents: """A model of temperature diffusion over a rectangular plate."""
  import numpy as np
  import yaml
  
  
  class Diffusion(object):
      """Model of temperature diffusion on a plate."""
  
      def __init__(self, config_file=None):
          """Initialize the model."""
  
          if config_file is not None:
              with open(config_file, 'r') as fp:
                  parameters = yaml.load(fp)
              for key, value in parameters.items():
                  setattr(self, key, value)
          else:
              self.nx = 8
              self.ny = 6
              self.dx = 1.0
              self.dy = 1.0
              self.alpha = 0.9
  
          self.time = 0.0
          self.dt = min(self.dx, self.dy) ** 2.0 / (4.0 * self.alpha)
          self.dt /= 2.0
  
          self.temperature = np.zeros((self.ny, self.nx))
          self.new_temperature = self.temperature.copy()
  
      def advance(self):
          """Advance the model by one time step."""
  
          self.solve()
          self.time += self.dt
  
      def solve(self):
          """Solve the diffusion equation."""
  
          dx2, dy2 = self.dx**2, self.dy**2
          coef = self.alpha * self.dt / (2.0*(dx2 + dy2))
  
          for i in range(1, self.ny-1):
              for j in range(1, self.nx-1):
                  self.new_temperature[i,j] = \
                      self.temperature[i,j] + coef * (
                      dx2*(self.temperature[i,j-1] + self.temperature[i,j+1]) +
                      dy2*(self.temperature[i-1,j] + self.temperature[i+1,j]) -
                      2.0*(dx2 + dy2)*self.temperature[i,j])
  
          self.new_temperature[(0, -1), :] = 0.0
          self.new_temperature[:, (0, -1)] = 0.0
  
          self.temperature[:] = self.new_temperature
  
subject: Change the number of default rows and cols