Le 10/08/2017 à 19:55, Samuel Gougeon a écrit :


Dear co-scilabers,

The bug 8297 <http://bugzilla.scilab.org/8297> reporting the outstanding slowness of the cat() function was reported in 2010 but lasts since cat() was introduced. As measured and commented in the report, this slowness actually makes cat() almost unusable, except for small sized arrays to be concatenated.

For instance, after M = rand(500,500); cat(3,M,M) takes more than 11 days (yes)
with Scilab 5.5.2, and roughly 4 hours with Scilab 6.0.0.

So, everyone could imagine how much Scilab currently takes just to build a standard 1000x1000 RGB image by stacking its 3 1000x1000 R,G,B layers using cat(3,R,G,B).
The current algorithm is exponential with respect to the array size...

Before using GPU routines to process images, a much simpler thing can be done
to enable cat() for true life usages : rewritting it.
This is what is done here: https://codereview.scilab.org/#/c/19278/

Some rewievers are needed to make cat() truly available in Scilab 6.0.1.
So, do not hesitate to contribute online.


To complete: This new implementation spends 0.25 s (instead of 4 hours) to execute

M = rand(500,500);
cat(3,M,M);

and 0.42 s to process

M = rand(1000,1000);
cat(3,M,M,M);

Doesn't it fit more to what could be expected?
SG

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