yi[i] is the list of derivatives known at xi[i]. Of length N.
x : scalar or array_like
Of length M.
der : integer or list
How many derivatives to extract; None for all potentially
nonzero derivatives (that is a number equal to the number
of points), or a list of derivatives to extract. This number
includes the function value as 0th derivative.
axis : int, optional
Axis in the yi array corresponding to the x-coordinate values.