On Wed, Mar 26, 2008 at 5:22 PM, Andreas Klöckner <lists@informa.tiker.net> wrote:
Hi all,
The docstring for vander() seems to contradict what the function does. In particular, the columns in the vander() output seem reversed wrt its docstring. I feel like one of the two needs to be fixed, or is there something I'm not seeing?
This here is fresh from the Numpy examples page:
8< docstring ----------------------------------------------- X = vander(x,N=None)
The Vandermonde matrix of vector x. The i-th column of X is the the i-th power of x. N is the maximum power to compute; if N is None it defaults to len(x).
8< Example -------------------------------------------------
from numpy import * x = array([1,2,3,5]) N=3 vander(x,N) # Vandermonde matrix of the vector x array([[ 1, 1, 1], [ 4, 2, 1], [ 9, 3, 1], [25, 5, 1]]) 8< ---------------------------------------------------------
The docstring is incorrect. The Vandermonde matrix produced is compatible with numpy polynomials that also go from high to low powers. I would have done it the other way round, so index matched power, but that isn't how it is. Chuck