ccolamd_example.c

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/* ========================================================================== */
/* === ccolamd and csymamd example ========================================== */
/* ========================================================================== */

/* ----------------------------------------------------------------------------
 * CCOLAMD Copyright (C), Univ. of Florida.  Authors: Timothy A. Davis,
 * Sivasankaran Rajamanickam, and Stefan Larimore
 * -------------------------------------------------------------------------- */

/*
 *  ccolamd example of use, to order the columns of a 5-by-4 matrix with
 *  11 nonzero entries in the following nonzero pattern, with default knobs
 *  and no ordering constraints.
 *
 *     x 0 x 0
 *     x 0 x x
 *     0 x x 0
 *     0 0 x x
 *     x x 0 0
 *
 *  csymamd example of use, to order the rows and columns of a 5-by-5
 *  matrix with 13 nonzero entries in the following nonzero pattern,
 *  with default knobs and no ordering constraints.
 *
 *     x x 0 0 0
 *     x x x x 0
 *     0 x x 0 0
 *     0 x 0 x x
 *     0 0 0 x x
 *
 *  (where x denotes a nonzero value).
 */

/* ========================================================================== */

#include <stdio.h>
#include "ccolamd.h"

#define A_NNZ 11
#define A_NROW 5
#define A_NCOL 4
#define ALEN 150    /* size max (2.2*nnz+17*ncol+7*nrow+6, 23*ncol+7*nrow+6) */

#define B_NNZ 4
#define B_N 5

int main (void)
{

    /* ====================================================================== */
    /* input matrix A definition */
    /* ====================================================================== */

    int A [ALEN] = {

        0, 1, 4,                /* row indices of nonzeros in column 0 */
        2, 4,                   /* row indices of nonzeros in column 1 */
        0, 1, 2, 3,             /* row indices of nonzeros in column 2 */
        1, 3} ;                 /* row indices of nonzeros in column 3 */

    int p [ ] = {

        0,                      /* column 0 is in A [0..2] */
        3,                      /* column 1 is in A [3..4] */ 
        5,                      /* column 2 is in A [5..8] */
        9,                      /* column 3 is in A [9..10] */
        A_NNZ} ;                /* number of nonzeros in A */

    /* ====================================================================== */
    /* input matrix B definition */
    /* ====================================================================== */

    int B [ ] = {               /* Note: only strictly lower triangular part */
                                /* is included, since symamd ignores the */
                                /* diagonal and upper triangular part of B. */

        1,                      /* row indices of nonzeros in column 0 */
        2, 3,                   /* row indices of nonzeros in column 1 */
                                /* row indices of nonzeros in column 2 (none) */
        4                       /* row indices of nonzeros in column 3 */
        } ;                     /* row indices of nonzeros in column 4 (none) */

    int q [ ] = {

        0,                      /* column 0 is in B [0] */
        1,                      /* column 1 is in B [1..2] */ 
        3,                      /* column 2 is empty */
        3,                      /* column 3 is in B [3] */
        4,                      /* column 4 is empty */
        B_NNZ} ;                /* number of nonzeros in strictly lower B */

    /* ====================================================================== */
    /* other variable definitions */
    /* ====================================================================== */

    int perm [B_N+1] ;          /* note the size is N+1 */
    int stats [CCOLAMD_STATS] ; /* for ccolamd and csymamd output statistics */

    int row, col, pp, length, ok ;

    /* ====================================================================== */
    /* dump the input matrix A */
    /* ====================================================================== */

    printf ("ccolamd %d-by-%d input matrix:\n", A_NROW, A_NCOL) ;
    for (col = 0 ; col < A_NCOL ; col++)
    {
        length = p [col+1] - p [col] ;
        printf ("Column %d, with %d entries:\n", col, length) ;
        for (pp = p [col] ; pp < p [col+1] ; pp++)
        {
            row = A [pp] ;
            printf ("    row %d\n", row) ;
        }
    }

    /* ====================================================================== */
    /* order the matrix.  Note that this destroys A and overwrites p */
    /* ====================================================================== */

    ok = ccolamd (A_NROW, A_NCOL, ALEN, A, p, (double *) NULL, stats, NULL) ;
    ccolamd_report (stats) ;

    if (!ok)
    {
        printf ("ccolamd error!\n") ;
        exit (1) ;
    }

    /* ====================================================================== */
    /* print the column ordering */
    /* ====================================================================== */

    printf ("ccolamd column ordering:\n") ;
    printf ("1st column: %d\n", p [0]) ;
    printf ("2nd column: %d\n", p [1]) ;
    printf ("3rd column: %d\n", p [2]) ;
    printf ("4th column: %d\n", p [3]) ;

    /* ====================================================================== */
    /* dump the strictly lower triangular part of symmetric input matrix B */
    /* ====================================================================== */

    printf ("\n\ncsymamd %d-by-%d input matrix:\n", B_N, B_N) ;
    printf ("Entries in strictly lower triangular part:\n") ;
    for (col = 0 ; col < B_N ; col++)
    {
        length = q [col+1] - q [col] ;
        printf ("Column %d, with %d entries:\n", col, length) ;
        for (pp = q [col] ; pp < q [col+1] ; pp++)
        {
            row = B [pp] ;
            printf ("    row %d\n", row) ;
        }
    }

    /* ====================================================================== */
    /* order the matrix B.  Note that this does not modify B or q. */
    /* ====================================================================== */

    ok = csymamd (B_N, B, q, perm, (double *) NULL, stats, &calloc, &free,
            NULL, -1) ;
    csymamd_report (stats) ;

    if (!ok)
    {
        printf ("csymamd error!\n") ;
        exit (1) ;
    }

    /* ====================================================================== */
    /* print the symmetric ordering */
    /* ====================================================================== */

    printf ("csymamd column ordering:\n") ;
    printf ("1st row/column: %d\n", perm [0]) ;
    printf ("2nd row/column: %d\n", perm [1]) ;
    printf ("3rd row/column: %d\n", perm [2]) ;
    printf ("4th row/column: %d\n", perm [3]) ;
    printf ("5th row/column: %d\n", perm [4]) ;

    return (0) ;
}