[Help-gsl] more than one submatrix of the same matrix?

[Eduardo Zacarías B.]

Hi!

I have come across some very particular problem:

I need to manipulate different rows of a matrix and I made two pointers 
pointing to the address of the matrix part of some views, created by the 
submatrix function. Curiously enough, the view seems to be overwritten 
by a newly created view, even if they point to different rows. I have 
looked at the documentation and didn't find anything saying that I 
couldn't create two independent views of the same matrix. That, or I'm 
really blind...

However, I have not tried to create vector views.

The following code illustrates the problem. The original annoyances 
happened with complex matrices

Platform is Slackware Linux 9 with locally compiled GSL 1.3 (gcc 3.2.2)

Any light on is highly appreciated. It's been several hours trying to 
figure out this.

Thank you very much!

Eduardo




code follows:
---------------------------------------------------
#include "all_the_includes.h"

int showMat(gsl_matrix *mat);

int main() {

gsl_matrix *mat = gsl_matrix_calloc(3,2);
gsl_matrix_set(mat,0,0,1);
gsl_matrix_set(mat,0,1,2);
gsl_matrix_set(mat,1,0,3);
gsl_matrix_set(mat,1,1,4);
gsl_matrix_set(mat,2,0,5);
gsl_matrix_set(mat,2,1,6);

std::cout << "Original matrix:\n\n";
showMat(mat);

std::cout << "Slicing second row\n";
gsl_matrix *secondRow = &gsl_matrix_submatrix(mat,1,0,1,mat->size2).matrix;

showMat(secondRow);

std::cout << "Slicing third row\n";
gsl_matrix *thirdRow = &gsl_matrix_submatrix(mat,2,0,1,mat->size2).matrix;

showMat(thirdRow);

std::cout << "Showing slice of the second row again:\n";
showMat(secondRow);

}


int showMat(gsl_matrix *mat) {
        for (int row = 0; row < mat->size1; ++row) {
                for (int col = 0; col < mat->size2; ++col) {
                        std::cout << gsl_matrix_get(mat,row,col) << " ";
                }
                std::cout << "\n";
        }
        std::cout << "\n";
}

---------------------------------------------------

And the output is:

---------------------------------------------------
Original matrix:

1 2
3 4
5 6

Slicing second row
3 4

Slicing third row
5 6

Showing slice of the second row again:
5 6