Re: [Scilab-users] unusable cat() rewritten. Call for reviewers

[Samuel Gougeon]

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


Dear co-scilabers,

The bug 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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[Scilab-users] unusable cat() rewritten. Call for reviewers

[Samuel Gougeon]

Dear co-scilabers,

The bug 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.

Thank you.
Samuel

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