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//------------------------------------------------------------------------------
// gb_get_sparsity: determine the sparsity of a matrix result
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
// gb_get_sparsity determines the sparsity of a result matrix C, which may be
// computed from one or two input matrices A and B. The following rules are
// used, in order:
// (1) GraphBLAS operations of the form C = GrB.method (Cin, ...) use the
// sparsity of Cin for the new matrix C.
// (2) If the sparsity is determined by the descriptor to the method, then that
// determines the sparsity of C.
// (3) If both A and B are present and both matrices (not scalars), the
// sparsity of C is A_sparsity | B_sparsity
// (4) If A is present (and not a scalar), then the sparsity of C is A_sparsity.
// (5) If B is present (and not a scalar), then the sparsity of C is B_sparsity.
// (6) Otherwise, the global default sparsity is used for C.
#include "gb_interface.h"
GxB_Format_Value gb_get_sparsity // 0 to 15
(
GrB_Matrix A, // may be NULL
GrB_Matrix B, // may be NULL
int sparsity_default // may be 0
)
{
int sparsity ;
int A_sparsity = 0 ;
int B_sparsity = 0 ;
GrB_Index nrows, ncols ;
//--------------------------------------------------------------------------
// get the sparsity of the matrices A and B
//--------------------------------------------------------------------------
if (A != NULL)
{
OK (GrB_Matrix_nrows (&nrows, A)) ;
OK (GrB_Matrix_ncols (&ncols, A)) ;
if (nrows > 1 || ncols > 1)
{
// A is a vector or matrix, not a scalar
OK (GxB_Matrix_Option_get (A, GxB_SPARSITY_CONTROL, &A_sparsity)) ;
}
}
if (B != NULL)
{
OK (GrB_Matrix_nrows (&nrows, B)) ;
OK (GrB_Matrix_ncols (&ncols, B)) ;
if (nrows > 1 || ncols > 1)
{
// B is a vector or matrix, not a scalar
OK (GxB_Matrix_Option_get (B, GxB_SPARSITY_CONTROL, &B_sparsity)) ;
}
}
//--------------------------------------------------------------------------
// determine the sparsity of C
//--------------------------------------------------------------------------
if (sparsity_default != 0)
{
// (2) the sparsity is defined by the descriptor to the method
sparsity = sparsity_default ;
}
else if (A_sparsity > 0 && B_sparsity > 0)
{
// (3) C is determined by the sparsity of A and B
sparsity = A_sparsity | B_sparsity ;
}
else if (A_sparsity > 0)
{
// (4) get the sparsity of A
sparsity = A_sparsity ;
}
else if (B_sparsity > 0)
{
// (5) get the sparsity of B
sparsity = B_sparsity ;
}
else
{
// (6) use the default sparsity
sparsity = GxB_AUTO_SPARSITY ;
}
return (sparsity) ;
}
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