code: def concat_t_vars(self):
          
          logger.warning('This function is deprecated and replaced by `concat_t_vars_np`.')
          out = np.array([])
  
          if len(self.t) == 0:
              return out
  
          out = np.ndarray(shape=(0, self.vars[0].size[0] + 1))
  
          for t, var in zip(self.t, self.vars):
              line = [[t]]
              line[0].extend(list(var))
              out = np.append(out, line, axis=0)
  
          return out
docs: Concatenate ``self.t`` with ``self.vars`` and output a single matrix
          for data dump
  
          :return matrix: concatenated matrix with ``self.t`` as the 0-th column