code: def set_var_index(self, name, index, var):
          
          tmp = self.get_var(name).copy()
          tmp.flat[index] = var
          self.set_var(name, tmp)
docs: Overwrite the values in variable "name" with data
          from var, at the flattened (C-contiguous style)
          indices. Indices is a vector of 0-based
          integers, of the same length as the vector var.
          For some implementations it can be equivalent
          and more efficient to do:
          `get_var(name).flat[index] = var`