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

[Samuel Gougeon]

Hello Stephane,

You can speed up by a factor larger than 100 just by calling v once (or 
3 times) instead of ~1000, as shown by this test:

function  test2()
    // part 1 : only 1 call to v
     v  =  rand(172,1);
     p  =  grand(1,839,"unf",1,173)
     tic()
     for  i=1:1000
         m1_v  =  v(p)
     end
     disp(toc())

    // part 2 : 839 calls to v
    e  =  "M1_v = ["+strcat("v("+string(p)+")")+"]"
     tic()
     for  i=1:1000
         execstr(e)
     end
     disp(toc())

    // part 3 : calls to "empty" execstr(), to be substrated from the previous result
    e  =  "M1_v = 0";
     tic()
     for  i=1:1000
         execstr(e)
     end
     disp(toc())
endfunction

On my PC, i get:
-->test2

     0.015

     1.888

     0.015

So, you do not really need to go to compiled solutions, just to rewrite 
839 lines into ~10 lines.

Regards
Samuel

Le 23/04/2015 23:51, 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)
> ]
>
> This kind of large vectors are the used to build a sparse matrix each 
> time the vector v changes, but with a constant sparsity pattern. 
> Actually, the time spent by Scilab in the statement
>
> M1=sparse(M1_ij,M1_v,[n1,n2])
>
> is negligible compared to the time spent to build f M1_v...
>
> I have also noticed that if you need to define such a matrix with more 
> that one column, the time elapsed is not linear with respect to the 
> number of columns: typically 4 times slower for 2 columns. In fact the 
> statement
>
> v=[1 1
> ...
> 1000 1000]
>
> is even two times slower than
>
> v1=[1
> ...
> 1000];
> v2=[1
> ....
> 1000];
> v=[v1 v2];
>
> So my question to users who have the experience of dynamic link of 
> user code : do you think that using dynamic link of compiled generated 
> C code could improve the timings ?
>
> In advance, thanks for your help !
>
> S.
>
>
>
>
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