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//------------------------------------------------------------------------------
// CAMD/Source/camd_preprocess: sort, remove duplicates, transpose a matrix
//------------------------------------------------------------------------------
// CAMD, Copyright (c) 2007-2022, Timothy A. Davis, Yanqing Chen, Patrick R.
// Amestoy, and Iain S. Duff. All Rights Reserved.
// SPDX-License-Identifier: BSD-3-clause
//------------------------------------------------------------------------------
/* Sorts, removes duplicate entries, and transposes from the nonzero pattern of
* a column-form matrix A, to obtain the matrix R. The input matrix can have
* duplicate entries and/or unsorted columns (CAMD_valid (n,Ap,Ai) must not be
* CAMD_INVALID).
*
* This input condition is NOT checked. This routine is not user-callable.
*/
#include "camd_internal.h"
/* ========================================================================= */
/* === CAMD_preprocess ===================================================== */
/* ========================================================================= */
/* CAMD_preprocess does not check its input for errors or allocate workspace.
* On input, the condition (CAMD_valid (n,n,Ap,Ai) != CAMD_INVALID) must hold.
*/
void CAMD_preprocess
(
Int n, /* input matrix: A is n-by-n */
const Int Ap [ ], /* size n+1 */
const Int Ai [ ], /* size nz = Ap [n] */
/* output matrix R: */
Int Rp [ ], /* size n+1 */
Int Ri [ ], /* size nz (or less, if duplicates present) */
Int W [ ], /* workspace of size n */
Int Flag [ ] /* workspace of size n */
)
{
/* --------------------------------------------------------------------- */
/* local variables */
/* --------------------------------------------------------------------- */
Int i, j, p, p2 ;
ASSERT (CAMD_valid (n, n, Ap, Ai) != CAMD_INVALID) ;
/* --------------------------------------------------------------------- */
/* count the entries in each row of A (excluding duplicates) */
/* --------------------------------------------------------------------- */
for (i = 0 ; i < n ; i++)
{
W [i] = 0 ; /* # of nonzeros in row i (excl duplicates) */
Flag [i] = EMPTY ; /* Flag [i] = j if i appears in column j */
}
for (j = 0 ; j < n ; j++)
{
p2 = Ap [j+1] ;
for (p = Ap [j] ; p < p2 ; p++)
{
i = Ai [p] ;
if (Flag [i] != j)
{
/* row index i has not yet appeared in column j */
W [i]++ ; /* one more entry in row i */
Flag [i] = j ; /* flag row index i as appearing in col j*/
}
}
}
/* --------------------------------------------------------------------- */
/* compute the row pointers for R */
/* --------------------------------------------------------------------- */
Rp [0] = 0 ;
for (i = 0 ; i < n ; i++)
{
Rp [i+1] = Rp [i] + W [i] ;
}
for (i = 0 ; i < n ; i++)
{
W [i] = Rp [i] ;
Flag [i] = EMPTY ;
}
/* --------------------------------------------------------------------- */
/* construct the row form matrix R */
/* --------------------------------------------------------------------- */
/* R = row form of pattern of A */
for (j = 0 ; j < n ; j++)
{
p2 = Ap [j+1] ;
for (p = Ap [j] ; p < p2 ; p++)
{
i = Ai [p] ;
if (Flag [i] != j)
{
/* row index i has not yet appeared in column j */
Ri [W [i]++] = j ; /* put col j in row i */
Flag [i] = j ; /* flag row index i as appearing in col j*/
}
}
}
#ifndef NDEBUG
ASSERT (CAMD_valid (n, n, Rp, Ri) == CAMD_OK) ;
for (j = 0 ; j < n ; j++)
{
ASSERT (W [j] == Rp [j+1]) ;
}
#endif
}
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