code: def _construct_approximation(self, basis_kwargs, coefs_list):
          
          derivs = self._construct_derivatives(coefs_list, **basis_kwargs)
          funcs = self._construct_functions(coefs_list, **basis_kwargs)
          return derivs, funcs
docs: Construct a collection of derivatives and functions that approximate
          the solution to the boundary value problem.
  
          Parameters
          ----------
          basis_kwargs : dict(str: )
          coefs_list : list(numpy.ndarray)
  
          Returns
          -------
          basis_derivs : list(function)
          basis_funcs : list(function)