/* ========================================================================== */
/* === BTF package ========================================================== */
/* ========================================================================== */
/* BTF_MAXTRANS: find a column permutation Q to give A*Q a zero-free diagonal
* BTF_STRONGCOMP: find a symmetric permutation P to put P*A*P' into block
* upper triangular form.
* BTF_ORDER: do both of the above (btf_maxtrans then btf_strongcomp).
*
* By Tim Davis. Copyright (c) 2004-2007, University of Florida.
* with support from Sandia National Laboratories. All Rights Reserved.
*/
/* ========================================================================== */
/* === BTF_MAXTRANS ========================================================= */
/* ========================================================================== */
/* BTF_MAXTRANS: finds a permutation of the columns of a matrix so that it has a
* zero-free diagonal. The input is an m-by-n sparse matrix in compressed
* column form. The array Ap of size n+1 gives the starting and ending
* positions of the columns in the array Ai. Ap[0] must be zero. The array Ai
* contains the row indices of the nonzeros of the matrix A, and is of size
* Ap[n]. The row indices of column j are located in Ai[Ap[j] ... Ap[j+1]-1].
* Row indices must be in the range 0 to m-1. Duplicate entries may be present
* in any given column. The input matrix is not checked for validity (row
* indices out of the range 0 to m-1 will lead to an undeterminate result -
* possibly a core dump, for example). Row indices in any given column need
* not be in sorted order. However, if they are sorted and the matrix already
* has a zero-free diagonal, then the identity permutation is returned.
*
* The output of btf_maxtrans is an array Match of size n. If row i is matched
* with column j, then A(i,j) is nonzero, and then Match[i] = j. If the matrix
* is structurally nonsingular, all entries in the Match array are unique, and
* Match can be viewed as a column permutation if A is square. That is, column
* k of the original matrix becomes column Match[k] of the permuted matrix. In
* MATLAB, this can be expressed as (for non-structurally singular matrices):
*
* Match = maxtrans (A) ;
* B = A (:, Match) ;
*
* except of course here the A matrix and Match vector are all 0-based (rows
* and columns in the range 0 to n-1), not 1-based (rows/cols in range 1 to n).
* The MATLAB dmperm routine returns a row permutation. See the maxtrans
* mexFunction for more details.
*
* If row i is not matched to any column, then Match[i] is == -1. The
* btf_maxtrans routine returns the number of nonzeros on diagonal of the
* permuted matrix.
*
* In the MATLAB mexFunction interface to btf_maxtrans, 1 is added to the Match
* array to obtain a 1-based permutation. Thus, in MATLAB where A is m-by-n:
*
* q = maxtrans (A) ; % has entries in the range 0:n
* q % a column permutation (only if sprank(A)==n)
* B = A (:, q) ; % permuted matrix (only if sprank(A)==n)
* sum (q > 0) ; % same as "sprank (A)"
*
* This behaviour differs from p = dmperm (A) in MATLAB, which returns the
* matching as p(j)=i if row i and column j are matched, and p(j)=0 if column j
* is unmatched.
*
* p = dmperm (A) ; % has entries in the range 0:m
* p % a row permutation (only if sprank(A)==m)
* B = A (p, :) ; % permuted matrix (only if sprank(A)==m)
* sum (p > 0) ; % definition of sprank (A)
*
* This algorithm is based on the paper "On Algorithms for obtaining a maximum
* transversal" by Iain Duff, ACM Trans. Mathematical Software, vol 7, no. 1,
* pp. 315-330, and "Algorithm 575: Permutations for a zero-free diagonal",
* same issue, pp. 387-390. Algorithm 575 is MC21A in the Harwell Subroutine
* Library. This code is not merely a translation of the Fortran code into C.
* It is a completely new implementation of the basic underlying method (depth
* first search over a subgraph with nodes corresponding to columns matched so
* far, and cheap matching). This code was written with minimal observation of
* the MC21A/B code itself. See comments below for a comparison between the
* maxtrans and MC21A/B codes.
*
* This routine operates on a column-form matrix and produces a column
* permutation. MC21A uses a row-form matrix and produces a row permutation.
* The difference is merely one of convention in the comments and interpretation
* of the inputs and outputs. If you want a row permutation, simply pass a
* compressed-row sparse matrix to this routine and you will get a row
* permutation (just like MC21A). Similarly, you can pass a column-oriented
* matrix to MC21A and it will happily return a column permutation.
*/
#ifndef _BTF_H
#define _BTF_H
/* make it easy for C++ programs to include BTF */
#ifdef __cplusplus
extern "C" {
#endif
#include "SuiteSparse_config.h"
int btf_maxtrans /* returns # of columns matched */
(
/* --- input, not modified: --- */
int nrow, /* A is nrow-by-ncol in compressed column form */
int ncol,
int Ap [ ], /* size ncol+1 */
int Ai [ ], /* size nz = Ap [ncol] */
double maxwork, /* maximum amount of work to do is maxwork*nnz(A); no limit
* if <= 0 */
/* --- output, not defined on input --- */
double *work, /* work = -1 if maxwork > 0 and the total work performed
* reached the maximum of maxwork*nnz(A).
* Otherwise, work = the total work performed. */
int Match [ ], /* size nrow. Match [i] = j if column j matched to row i
* (see above for the singular-matrix case) */
/* --- workspace, not defined on input or output --- */
int Work [ ] /* size 5*ncol */
) ;
/* long integer version (all "int" parameters become "SuiteSparse_long") */
SuiteSparse_long btf_l_maxtrans (SuiteSparse_long, SuiteSparse_long,
SuiteSparse_long *, SuiteSparse_long *, double, double *,
SuiteSparse_long *, SuiteSparse_long *) ;
/* ========================================================================== */
/* === BTF_STRONGCOMP ======================================================= */
/* ========================================================================== */
/* BTF_STRONGCOMP finds the strongly connected components of a graph, returning
* a symmetric permutation. The matrix A must be square, and is provided on
* input in compressed-column form (see BTF_MAXTRANS, above). The diagonal of
* the input matrix A (or A*Q if Q is provided on input) is ignored.
*
* If Q is not NULL on input, then the strongly connected components of A*Q are
* found. Q may be flagged on input, where Q[k] < 0 denotes a flagged column k.
* The permutation is j = BTF_UNFLIP (Q [k]). On output, Q is modified (the
* flags are preserved) so that P*A*Q is in block upper triangular form.
*
* If Q is NULL, then the permutation P is returned so that P*A*P' is in upper
* block triangular form.
*
* The vector R gives the block boundaries, where block b is in rows/columns
* R[b] to R[b+1]-1 of the permuted matrix, and where b ranges from 1 to the
* number of strongly connected components found.
*/
int btf_strongcomp /* return # of strongly connected components */
(
/* input, not modified: */
int n, /* A is n-by-n in compressed column form */
int Ap [ ], /* size n+1 */
int Ai [ ], /* size nz = Ap [n] */
/* optional input, modified (if present) on output: */
int Q [ ], /* size n, input column permutation */
/* output, not defined on input */
int P [ ], /* size n. P [k] = j if row and column j are kth row/col
* in permuted matrix. */
int R [ ], /* size n+1. block b is in rows/cols R[b] ... R[b+1]-1 */
/* workspace, not defined on input or output */
int Work [ ] /* size 4n */
) ;
SuiteSparse_long btf_l_strongcomp (SuiteSparse_long, SuiteSparse_long *,
SuiteSparse_long *, SuiteSparse_long *, SuiteSparse_long *,
SuiteSparse_long *, SuiteSparse_long *) ;
/* ========================================================================== */
/* === BTF_ORDER ============================================================ */
/* ========================================================================== */
/* BTF_ORDER permutes a square matrix into upper block triangular form. It
* does this by first finding a maximum matching (or perhaps a limited matching
* if the work is limited), via the btf_maxtrans function. If a complete
* matching is not found, BTF_ORDER completes the permutation, but flags the
* columns of P*A*Q to denote which columns are not matched. If the matrix is
* structurally rank deficient, some of the entries on the diagonal of the
* permuted matrix will be zero. BTF_ORDER then calls btf_strongcomp to find
* the strongly-connected components.
*
* On output, P and Q are the row and column permutations, where i = P[k] if
* row i of A is the kth row of P*A*Q, and j = BTF_UNFLIP(Q[k]) if column j of
* A is the kth column of P*A*Q. If Q[k] < 0, then the (k,k)th entry in P*A*Q
* is structurally zero.
*
* The vector R gives the block boundaries, where block b is in rows/columns
* R[b] to R[b+1]-1 of the permuted matrix, and where b ranges from 1 to the
* number of strongly connected components found.
*/
int btf_order /* returns number of blocks found */
(
/* --- input, not modified: --- */
int n, /* A is n-by-n in compressed column form */
int Ap [ ], /* size n+1 */
int Ai [ ], /* size nz = Ap [n] */
double maxwork, /* do at most maxwork*nnz(A) work in the maximum
* transversal; no limit if <= 0 */
/* --- output, not defined on input --- */
double *work, /* return value from btf_maxtrans */
int P [ ], /* size n, row permutation */
int Q [ ], /* size n, column permutation */
int R [ ], /* size n+1. block b is in rows/cols R[b] ... R[b+1]-1 */
int *nmatch, /* # nonzeros on diagonal of P*A*Q */
/* --- workspace, not defined on input or output --- */
int Work [ ] /* size 5n */
) ;
SuiteSparse_long btf_l_order (SuiteSparse_long, SuiteSparse_long *,
SuiteSparse_long *, double , double *, SuiteSparse_long *,
SuiteSparse_long *, SuiteSparse_long *, SuiteSparse_long *,
SuiteSparse_long *) ;
/* ========================================================================== */
/* === BTF marking of singular columns ====================================== */
/* ========================================================================== */
/* BTF_FLIP is a "negation about -1", and is used to mark an integer j
* that is normally non-negative. BTF_FLIP (-1) is -1. BTF_FLIP of
* a number > -1 is negative, and BTF_FLIP of a number < -1 is positive.
* BTF_FLIP (BTF_FLIP (j)) = j for all integers j. UNFLIP (j) acts
* like an "absolute value" operation, and is always >= -1. You can test
* whether or not an integer j is "flipped" with the BTF_ISFLIPPED (j)
* macro.
*/
#define BTF_FLIP(j) (-(j)-2)
#define BTF_ISFLIPPED(j) ((j) < -1)
#define BTF_UNFLIP(j) ((BTF_ISFLIPPED (j)) ? BTF_FLIP (j) : (j))
/* ========================================================================== */
/* === BTF version ========================================================== */
/* ========================================================================== */
/* All versions of BTF include these definitions.
* As an example, to test if the version you are using is 1.2 or later:
*
* if (BTF_VERSION >= BTF_VERSION_CODE (1,2)) ...
*
* This also works during compile-time:
*
* #if (BTF >= BTF_VERSION_CODE (1,2))
* printf ("This is version 1.2 or later\n") ;
* #else
* printf ("This is an early version\n") ;
* #endif
*/
#define BTF_DATE "Jun 1, 2012"
#define BTF_VERSION_CODE(main,sub) ((main) * 1000 + (sub))
#define BTF_MAIN_VERSION 1
#define BTF_SUB_VERSION 2
#define BTF_SUBSUB_VERSION 0
#define BTF_VERSION BTF_VERSION_CODE(BTF_MAIN_VERSION,BTF_SUB_VERSION)
#ifdef __cplusplus
}
#endif
#endif