[Scilab-users] Ways to speed up simple things in Scilab ?

[Stéphane Mottelet]

Le 24/04/2015 15:35, Samuel Gougeon a écrit :
> Le 24/04/2015 14:50, Stéphane Mottelet a écrit :
>> Hello Antoine
>>
>> I think your idea is excellent in my context, I Will try it and keep 
>> you informed of the actual improvement,
>>
>> S.
>>
>> Le 24 avr. 2015 à 13:31, Antoine Monmayrant 
>> <antoine.monmayrant at laas.fr <mailto:antoine.monmayrant at laas.fr>> a 
>> écrit :
>>
>>> Hi again,
>>>
>>> Another way you might improve your code: can you write it as a 
>>> matrix-vector product?
>>> Like
>>>
>>> M1_v=A*v;
>>> Where A is a matrix of size (839,172) that corresponds to your weird 
>>> combination of v(i) to build M1_v.
>>> It seems to me that you should be able to write it that way, which 
>>> would save a lot of time as matrix product are fast in Scilab.
>
> The test:
> A  =  sign(sprand(839,172,2/172,  "normal"));
> i  =  A>0;  A(i)  =  1;
> i  =  A<0;  A(i)  =  -1;
> p  =  rand(172,1);
> tic()
> for  i  =  1:1000
>      M1_v  =  A*p;
> end
> toc()
> gives
> -->toc()
>  ans  =
>     0.156
>
> But somewhere you will somehow have to actually preset
> A(1,17) = 1;
> A(2,104) = 1;
> A(3,149) = 1;
> A(4, [18 63 103]) = -1;
> A(5, [18 63 103]) = -1;
> A(6,17) = 1;
> ...
> A(838, 104) = 1;
> A(839, 149) = 1;
>
> A priori, this is a bit more human-readable, but also more 
> time-consuming... I am afraid that doing this in this way you will 
> loose the gain "got" with matrix multiplication.
>
> Samuel

No it is not a problem because the A matrix has to be created only once, 
since its sparsity pattern won't change later on.

S.

>
>>>
>>> Antoine
>>>
>>>
>>> Le 04/23/2015 11:51 PM, Stéphane Mottelet a écrit :
>>>> Hello,
>>>>
>>>> I am currently working on a project where Scilab code is 
>>>> automatically generated, and after many code optimization, the 
>>>> remaining bottleneck is the time that Scilab spends to execute 
>>>> simple code like this (full script (where the vector has 839 lines) 
>>>> with timings is attached) :
>>>>
>>>> M1_v=[v(17)
>>>> v(104)
>>>> v(149)
>>>> -(v(18)+v(63)+v(103))
>>>> -(v(18)+v(63)+v(103))
>>>> v(17)
>>>> ...
>>>> v(104)
>>>> v(149)
>>>> ]
>>>> .../...
>
>
>
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