CODEWITHSUNDEEP
cgsl
gypaetus
gypaetus

Reputation: 7349

Initialize elements of GSL matrix

I have allocated a large gsl_matrix and would like to allocate all its elements with known float values. Is there a way to do it without using gsl_matrix_set for each element? I am looking for the equivalent of fortran's reshape function to initialize a matrix.

A = reshape( (/0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7,
0, 1, 2, 3, 4, 5, 6, 7/), (/ 8, 8/) )

Upvotes: 1

Views: 2197

Answers (1)

Bernhard Bodenstorfer
Bernhard Bodenstorfer

Reputation: 960

Matrices only support limited setting of all values, that is by gsl_matrix_set_all, gsl_matrix_set_zero or gsl_matrix_set_identity.

However, you can create and initialise an array and then create a matrix view from that using gsl_matrix_view_array, gsl_matrix_const_view_array, gsl_matrix_view_array_with_tda or gsl_matrix_const_view_array_with_tda. (Matrix views are common in GSL. For example, they are used to express sub-matrices returned by gsl_matrix_submatrix.) The matrix view is a struct which contains a field matrix upon which you execute the gsl_matrix methods you wish to apply.

For example, compile with gcc matrixview.c -lgsl -lgslcblas the following file matrixview.c:

#include <stdio.h>
#include <gsl/gsl_matrix.h>

#define rows 2
#define cols 3

int main () {
    const double data[rows*cols] = { 
        0.0, 0.1, 0.2,
        1.0, 1.1, 1.2,
    };  
    const gsl_matrix_const_view mat = gsl_matrix_const_view_array( data, rows, cols );
    for ( size_t row = 0; row < rows; ++row ) { 
        for ( size_t col = 0; col < cols; ++col ) { 
            printf( "\t%3.1f", gsl_matrix_get( &mat.matrix, row, col ) );
        }
        printf( "\n" );
    }
}

Upvotes: 2

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