def setup(delta_x, delta_y, delta_z, pos)
      # Set up the provided parameters:
      @delta_x = delta_x
      @delta_y = delta_y
      @delta_z = delta_z
      self.pos = pos
      # Set up the dimensional parameters:
      @nx, @ny, @nz = self.shape
    end
def setup(delta_x, delta_y, delta_z, pos)
      # Set up the provided parameters:
      @delta_x = delta_x
      @delta_y = delta_y
      @delta_z = delta_z
      self.pos = pos
      # Set up the dimensional parameters:
      @nx, @ny, @nz = self.shape
    end
Sets up the instance variables.