docs: def sum2diag(A, D, out=None):
      r"""Add values ``D`` to the diagonal of matrix ``A``.
  
      Args:
          A (array_like): Left-hand side.
          D (array_like or float): Values to add.
          out (:class:`numpy.ndarray`, optional): copy result to.
  
      Returns:
          :class:`numpy.ndarray`: Resulting matrix.
      """
      A = asarray(A, float)
      D = asarray(D, float)
      if out is None:
          out = copy(A)
      else:
          copyto(out, A)
      einsum("ii->i", out)[:] += D
      return out