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//------------------------------------------------------------------------------
// GB_convert_bitmap_to_sparse_test: test conversion of bitmap to sparse
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
// Returns true if a bitmap matrix should be converted to sparse.
// Returns false if the matrix should stay bitmap.
// If A is m-by-n and A->sparsity_control is GxB_ANY_SPARSITY with b =
// A->bitmap_switch, the matrix switches to bitmap if nnz(A)/(m*n) > b. A
// bitmap matrix switches to sparse if nnz(A)/(m*n) <= b/2. A matrix whose
// density is between b/2 and b remains in its current state.
// A->bitmap_switch is normally a fraction in range 0 to 1. A value of 1
// ensures that A is never converted to bitmap.
// These default rules may change in future releases of SuiteSparse:GraphBLAS.
// If this test returns true and the matrix changes to sparse, then the rule
// for A->hyper_switch may then convert it from sparse to hypersparse.
#include "GB.h"
bool GB_convert_bitmap_to_sparse_test // test for hyper/sparse to bitmap
(
float bitmap_switch, // A->bitmap_switch
int64_t anz, // # of entries in A = GB_nnz (A)
int64_t vlen, // A->vlen
int64_t vdim // A->vdim
)
{
// current number of entries in the matrix or vector
float nnz = (float) anz ;
// maximum number of entries in the matrix or vector
float nnz_dense = ((float) vlen) * ((float) vdim) ;
// A should switch to sparse if the following condition is true:
return (nnz <= (bitmap_switch/2) * nnz_dense) ;
}
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