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

[aweeks at hidglobal.com]

Hello Stephane,

We have a Scilab program which performs a  numerical integration on data 
points in 3-dimensions - it has two nested loops.  When the number of data 
points was large this was slow so we implemented the calculation function 
in C and got a speed improvement of about 24 times !

We also found three other improvements:

        using pointer arithmetic was faster than 'for' loops,
        'pow(x, 2)' was faster than x*x,
        handling the data as 3 (N x 1) vectors was faster than using 1 (N 
x 3) matrix.

each of these giving something like a 3-4% improvement - small compared to 
x24 but still worth having.

If you don't mind tackling the dynamic linking it's probably worth the 
effort if you'll use this program a few times - good luck.

Adrian.


Adrian Weeks 
Development Engineer, Hardware Engineering EMEA
Office: +44 (0)2920 528500 | Desk: +44 (0)2920 528523 | Fax: +44 (0)2920 
520178
aweeks at hidglobal.com


Unit 3, Cae Gwyrdd,
Green meadow Springs,
Cardiff, UK,
CF15 7AB.
www.hidglobal.com




From:
Stéphane Mottelet <stephane.mottelet at utc.fr>
To:
"International users mailing list for Scilab." <users at lists.scilab.org>
Date:
23/04/2015 22:52
Subject:
[Scilab-users] Ways to speed up simple things in Scilab ?
Sent by:
"users" <users-bounces at lists.scilab.org>



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.


[attachment "test.sce" deleted by Adrian Weeks/CWL/EU/ITG] 
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