`kmeans' undefined near line 7 column 8

[zetah]

Hi,

I use octave-3.6.2 on XP 32bit.
I'm trying to run a script, but I get an error which doesn't seem to be indexed by Google.

Here it is:

========================================
im = imread('test.png');
r = reshape(im, [size(im,1) * size(im,2),3]);

[k,c] = kmeans(double(r),20);
========================================

which gives me this error:

========================================
error: `kmeans' undefined near line 7 column 8
========================================

Can anyone point me what is causing this error and how to resolve it?

TIA