[Numpy-discussion] Numpy performance vs Matlab.

Sturla Molden sturla@molden...
Fri Jan 9 13:44:03 CST 2009

> -2- Now with the code below I have strange result.
> With w=h=400:
>    - Using "slice"        =>  0.99 sec
>    - Using "numpy.ogrid"  =>  0.01 sec

It is not equivalent. The ogrid version only uses diagonal elements, and
does less work.

> It seems "ogrid" got better performance, but broadcasting is not working
> any
> more.

Broadcasting is working, but not the way you think. Ogrid is not a faster
alternative to slicing.

You have the same in Matlab. You can index with a slice, an array of
indices, or an array of booleans. If you are going to use the second
alternative, the shape of the index arrays -- in each dimension -- must
equal that of the output. You cannot use a "meshgrid" with different
shaped arrays of x, y and z indices. NumPy is no different from Matlab

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