[Scilab-users] Interfacing fortran code with scilab

[Pierre Vuillemin]

I am quite used to work with Matlab, hence my code is fully vectorized,
however :
- some parts of my code cannot be vectorized (optimization loops, etc)
- some other parts are really not natural when written in a vectorized
way. Thus writting, reading, debugging and maintaining them is a pain.

But basically, I just would like to see the speed gain I can achieve
with a lower level language on some parts of my code.
Then depending on the performances of the forthcoming JIT compiler of
Scilab, I may consider to translate (or not) my code in fortran.

Pierre Vuillemin

Le mercredi 05 février 2014 à 12:38 +0000, Carrico, Paul a écrit :
> All
> 
>  before using fortan code, did you have a look to the "vectorization" in order to avoid loops (that drastically decrease speed)  and to increase speedup consequently ?
> 
> Just an advice
> 
> Paul
> 
> -----Message d'origine-----
> De : users [mailto:users-bounces at lists.scilab.org] De la part de Pierre Vuillemin
> Envoyé : mercredi 5 février 2014 09:56
> À : users at lists.scilab.org
> Objet : [Scilab-users] Interfacing fortran code with scilab
> 
> Hello all,
> 
> I am currently learning fortran in order to speed up some part o my code and I would like to interface it with Scilab.
> 
> To make some tests, I have used this fortran code :
> 
> subroutine matmul(C,A,B,m,n,p)
>     integer ::m,n,p,i,j,k
>     real(kind=8),dimension(m,n),intent(in)::A
>     real(kind=8),dimension(n,p),intent(in)::B
>     real(kind=8),dimension(m,p),intent(out)::C
>     real(kind=8):: temp
>     C = 0
>     do j =1,p
>       do k=1,n
>         temp = B(k,j)
>         do i=1,m
>             C(i,j)=C(i,j) + A(i,k)*temp
>         end do
>       end do
>     end do        
> end subroutine matmul
> 
> which performs a matrix multiplication. Then I have used 'ilib_for_link'
> to create the link.
> It works but I have some questions : 
> 
> - I did the same thing in Python with f2py and the code is seemingly faster in python, I was wondering why ? (the precision is the same)
> 
> - If I change the 'kind = 8' to 'kind = 4' in the fortran code, the function returns a result which completely wrong.
> I expected it to be wrong, but not that much : for instance, with A = 10 and B = 20, the call to the fortran function gives me '6.36D-314'  
> What is the reason? (My comprehension of how fortran types work with the kind parameter is still limited, I know that kind=8 and kind=4 is not a very portable expression though)
> 
> - If I replace
>     real(kind=8),dimension(m,p),intent(out)::C
> by
>     real(kind=8),dimension(:,:),intent(out)::C
> I get a segfault in Scilab or it just closes. I was wondering why ? (I thought it was something valid since gfortran still compiles)
> 
> - Is it possible to keep the upper case in the name of fortran functions when linked to scilab ? (At the beginning, my function was called 'matMul' and it took me some time to figure out what the error message 'matMul is not an entry point' meant)
> 
> Best regards,
> 
> Pierre Vuillemin
> 
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