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// CXSparse/Source/cs_symperm: symmetric permutation of a sparse matrix
// CXSparse, Copyright (c) 2006-2022, Timothy A. Davis. All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
#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 */
}
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