cs_symperm.c

/*
 * CXSPARSE: a Concise Sparse Matrix package - Extended.
 * Copyright (c) 2006-2009, Timothy A. Davis.
 * http://www.cise.ufl.edu/research/sparse/CXSparse
 * 
 * CXSparse is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * CXSparse is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this Module; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "cs.h"
/* C = A(p,p) where A and C are symmetric the upper part stored; pinv not p */
cs *cs_symperm (const cs *A, const CS_INT *pinv, CS_INT values)
{
    CS_INT i, j, p, q, i2, j2, n, *Ap, *Ai, *Cp, *Ci, *w ;
    CS_ENTRY *Cx, *Ax ;
    cs *C ;
    if (!CS_CSC (A)) return (NULL) ;                    /* check inputs */
    n = A->n ; Ap = A->p ; Ai = A->i ; Ax = A->x ;
    C = cs_spalloc (n, n, Ap [n], values && (Ax != NULL), 0) ; /* alloc result*/
    w = cs_calloc (n, sizeof (CS_INT)) ;                   /* get workspace */
    if (!C || !w) return (cs_done (C, w, NULL, 0)) ;    /* out of memory */
    Cp = C->p ; Ci = C->i ; Cx = C->x ;
    for (j = 0 ; j < n ; j++)           /* count entries in each column of C */
    {
        j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
        for (p = Ap [j] ; p < Ap [j+1] ; p++)
        {
            i = Ai [p] ;
            if (i > j) continue ;       /* skip lower triangular part of A */
            i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
            w [CS_MAX (i2, j2)]++ ;     /* column count of C */
        }
    }
    cs_cumsum (Cp, w, n) ;              /* compute column pointers of C */
    for (j = 0 ; j < n ; j++)
    {
        j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
        for (p = Ap [j] ; p < Ap [j+1] ; p++)
        {
            i = Ai [p] ;
            if (i > j) continue ;       /* skip lower triangular part of A*/
            i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
            Ci [q = w [CS_MAX (i2, j2)]++] = CS_MIN (i2, j2) ;
            if (Cx) Cx [q] = (i2 <= j2) ? Ax [p] : CS_CONJ (Ax [p]) ;
        }
    }
    return (cs_done (C, w, NULL, 1)) ;  /* success; free workspace, return C */
}