code: def _add_fixed_dim(self, fixed_dim=-1):
          
  
          if fixed_dim in [-1, None, 'last']:
              fixed_dim = len(self.input_image.shape) - 1  # last dimension
  
          if int(fixed_dim)!=fixed_dim or \
              fixed_dim > len(self.input_image.shape) or \
              fixed_dim < -1:
              raise ValueError('invalid value for the dimension to be fixed!'
                               'Must be an integer in range [0, {}] inclusive'
                               ''.format(len(self.input_image.shape)))
  
          if self.input_image.shape[fixed_dim] < 2:
              raise ValueError('Input image must have atleast two samples '
                               'in the fixed dimension. It has {}. '
                               'Full image shape: {} '
                               ''.format(self.input_image.shape[fixed_dim],
                                         self.input_image.shape))
  
          self.fixed_dim = int(fixed_dim)
docs: Makes note of which dimension needs to be fixed, defaulting to last.