[scilab-Users] SciLab question dealing with linear algebra / tensor multiplication.

[vincent.lejeune at scilab.org]

A(1,:,:) is considered as a 1*j*k matrix, which is not the same as a j*k
matrix, in Scilab 5.2.2.
I don't know the underlying reason of this behaviour, but it may be due to
storage constraint in memory : a j*k matrix is stored as a contigous array
of double.  A i*j*1 matrix is stored as a contigous array of double, too.
whereas a 1*j*k is stored as a sequence of padded array (with pad = i).

You can use the matrix() function :

B=matrix(A(1,:,:),j,k);

B is the j*k matrix that is equivalent to A(1,:,:). There is a memory copy
but the performance should stay OK.

Vincent

On Wed, 19 May 2010 19:41:51 +0200, Julien Colmars
<julien.colmars at imelavi.fr> wrote:
> Hi,
> 
> I've a SciLab problem dealing with* linear algebra / tensor
> multiplication.*
> 
> Let's say I have *a matrix A wich size is i * j * k* ( is it called a
> matrix
> in SciLab ? a 3rd order tensor ? a table ?...)
> 
> SciLab knows that *A(:,:,1) is a matrix*, and SciLab is able to multiply
it
> with another matrix...
> But it is *not the case of A(1,:,:)* for example.... which seems to be a
> table of 2 1x2 vectors. [at least in SciLab 4.2.1]
> 
> I'm looking for an elegant solution to avoid many loops... my
calculation
> is
> becoming too slow :
> 
> *So these are my questions :*
> 
>    - why it is not implemented in SciLab ? (sorry for this naive
> question)*Is there a specific reason not to authorize to build a
> matrix from table
>    values ?*
>    - *How could it be done* (call to external C/Fortran routine or
specific
>    linear algebra libraries) ?
>    - *Is it possible to simply make a permutation of two subscript* :
for
>    example from A(i,j,k) I want to get B = A(k,j,i) ? This way I could
>    make my
>    basic multiplications...
> 
> I hope it is clear enough...
> Thank you in advance for your help.
> 
> 
> 
> *Julien Colmars*
> 
> PhD student,
> Équipe Mécanique de l'Arbre et du Bois
> Laboratoire de Mécanique et Génie Civil
> Adresse :   LMGC - UMR5508
>                 Université Montpellier 2
>                 CC 048 Place Eugène Bataillon
>                 34090 Montpellier, France
> Tel. :         +33 (0)4 67 14 96 42
> Fax. :        +33 (0)4 67 14 47 92