Tutorial

Working with matrices

Download the source code and compile it - in the case of an installation in the own home directory - e.g. by :

gcc test1.c -O2 -march=athlon-xp -I $HOME/local/include -I $HOME/include/UMFPACK -L $HOME/local/lib $HOME/local/lib/libmeml.a -lm -llapack /usr/lib/libf2c.a -lumfpack -lamd -lcblas -lf77blas -latlas -o test1

/*
   This is a small example how to do
   matrix manipulation and matrix operations with meml

   more functions are documented under

   http://www.meml.smial.de/doc/group__meml__matrix__manipulation.html
   http://www.meml.smial.de/doc/group__meml__matrix__operatoren.html
*/

# include "meml.h"
# define SIZE 10000

int main (void)
{
    int i;
    M_TYPE A_type;
    MEML_INT A_row, A_col ;
    ME_MATRIX * DenseMatrix;
    ME_MATRIX * ListSparse;
    ME_MATRIX * Compressed;
    ME_MATRIX * A;
    MEML_FLOAT data[] ={1,3,7  ,  -1,0,1  ,  0, 0 ,5  ,  0,1,0};

    /* creating a matrix from an array of doubles */
    DenseMatrix=meml_matrix_new_form_carray(ND,4,3,data);

    /* creating an empty sparse matrix */
    ListSparse=meml_matrix_new(LS,SIZE,SIZE);

    /* setting up a tridiagonal matrix*/
    meml_matrix_element_set(ListSparse,0,0,42);
    meml_matrix_element_set(ListSparse,0,1,42);
    meml_matrix_element_set(ListSparse,0,1,42);

    meml_matrix_element_set(ListSparse,SIZE-1,SIZE-1,42);

    for (i=0;i<SIZE-1;i++)
    {
        meml_matrix_element_set(ListSparse,i,i,42);
        meml_matrix_element_set(ListSparse,i,i+1,-1);
        meml_matrix_element_set(ListSparse,i+1,i,1);
    }

    /* printing a matrix on the screen */
    printf("ListSparse = \n");
    meml_matrix_print(ListSparse);

    printf("DenseMatrix = \n");
    meml_matrix_print(DenseMatrix);

    /* scaling a matrix */
    meml_matrix_scaling_f(0.5,DenseMatrix);
    printf("DenseMatrix (scaled) = \n");
    meml_matrix_print(DenseMatrix);

    /* rounding towards plus infinity */
    meml_matrix_ceil (DenseMatrix);
    printf("DenseMatrix (after ceil) = \n");
    meml_matrix_print(DenseMatrix);

    /* converting a matrix to a new type ... */
    Compressed = meml_matrix_convert(CS,ListSparse);
    /* ... and scaling it */
    meml_matrix_scaling_f(1.0/42.0,Compressed);

    /* adding two matrices */
    A=meml_matrix_add(Compressed,ListSparse);
    /* in most cases it is faster not to mix
       the different matrix formats but it works */

    /* now let's have a look what we get */
    meml_matrix_property_get (A, &A_col, &A_row, &A_type);
    /* the resulting matrix format of meml_matrix_add is not defined
       but it will be sparse matrix type and in this case
       it should be a list based sparse matrix type
    */
    if (A_type == LS)
        printf("List Sparse\n");
    else if (A_type == CS)
        printf("Compressed Sparse\n");
    else if (A_type == ND)
        printf("Dense Matrix\n");

    /* finally let's change some more
       single values in a matrix */

    meml_matrix_element_add(DenseMatrix,0,0,28);
    meml_matrix_element_mul(DenseMatrix,2,2,13);

    printf("DenseMatrix (at last) = \n");
    meml_matrix_print(DenseMatrix);

    meml_matrix_free(A);
    meml_matrix_free(DenseMatrix);
    meml_matrix_free(ListSparse);
    meml_matrix_free(Compressed);

    exit(EXIT_SUCCESS);
}

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