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//------------------------------------------------------------------------------
// LAGraph_Cached_IsSymmetricStructure: determine G->is_symmetric_structure
//------------------------------------------------------------------------------
// LAGraph, (c) 2019-2022 by The LAGraph Contributors, All Rights Reserved.
// SPDX-License-Identifier: BSD-2-Clause
//
// For additional details (including references to third party source code and
// other files) see the LICENSE file or contact permission@sei.cmu.edu. See
// Contributors.txt for a full list of contributors. Created, in part, with
// funding and support from the U.S. Government (see Acknowledgments.txt file).
// DM22-0790
// Contributed by Timothy A. Davis, Texas A&M University
//------------------------------------------------------------------------------
// Also computes G->AT if not already computed, if G is not an undirected
// graph and G->A is square.
#define LG_FREE_WORK \
{ \
GrB_free (&S1) ; \
GrB_free (&S2) ; \
GrB_free (&C) ; \
}
#include "LG_internal.h"
int LAGraph_Cached_IsSymmetricStructure
(
// input/output:
LAGraph_Graph G, // graph to determine the symmetry of structure of A
char *msg
)
{
//--------------------------------------------------------------------------
// clear msg and check G
//--------------------------------------------------------------------------
GrB_Matrix C = NULL, S1 = NULL, S2 = NULL ;
LG_CLEAR_MSG_AND_BASIC_ASSERT (G, msg) ;
if (G->kind == LAGraph_ADJACENCY_UNDIRECTED)
{
// assume A is symmetric for an undirected graph
G->is_symmetric_structure = LAGraph_TRUE ;
return (GrB_SUCCESS) ;
}
if (G->is_symmetric_structure != LAGRAPH_UNKNOWN)
{
// cached symmetric property is already known
return (GrB_SUCCESS) ;
}
//--------------------------------------------------------------------------
// determine the size of A
//--------------------------------------------------------------------------
GrB_Matrix A = G->A ;
GrB_Index n, ncols ;
GRB_TRY (GrB_Matrix_nrows (&n, A)) ;
GRB_TRY (GrB_Matrix_ncols (&ncols, A)) ;
if (n != ncols)
{
// A is rectangular and thus cannot be symmetric
G->is_symmetric_structure = LAGraph_FALSE ;
return (GrB_SUCCESS) ;
}
//--------------------------------------------------------------------------
// compute the transpose, if not already computed
//--------------------------------------------------------------------------
if (G->AT == NULL)
{
LG_TRY (LAGraph_Cached_AT (G, msg)) ;
}
//--------------------------------------------------------------------------
// check if the structure of A and AT are the same
//--------------------------------------------------------------------------
GRB_TRY (GrB_Matrix_new (&C, GrB_BOOL, n, n)) ;
// C(i,j) = 1 if both A(i,j) and AT(i,j) exist
GRB_TRY (GrB_eWiseMult (C, NULL, NULL, GrB_ONEB_BOOL, A, G->AT, NULL)) ;
GrB_Index nvals1, nvals2 ;
GRB_TRY (GrB_Matrix_nvals (&nvals1, C)) ;
GRB_TRY (GrB_Matrix_nvals (&nvals2, A)) ;
G->is_symmetric_structure =
(nvals1 == nvals2) ? LAGraph_TRUE : LAGraph_FALSE ;
//--------------------------------------------------------------------------
// free workspace and return result
//--------------------------------------------------------------------------
LG_FREE_WORK ;
return (GrB_SUCCESS) ;
}