umf_lsolve.c
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/* ========================================================================== */
/* === UMF_lsolve =========================================================== */
/* ========================================================================== */
/* -------------------------------------------------------------------------- */
/* UMFPACK Copyright (c) Timothy A. Davis, CISE, */
/* Univ. of Florida. All Rights Reserved. See ../Doc/License for License. */
/* web: http://www.cise.ufl.edu/research/sparse/umfpack */
/* -------------------------------------------------------------------------- */
/* solves Lx = b, where L is the lower triangular factor of a matrix */
/* B is overwritten with the solution X. */
/* Returns the floating point operation count */
#include "umf_internal.h"
GLOBAL double UMF_lsolve
(
NumericType *Numeric,
Entry X [ ], /* b on input, solution x on output */
Int Pattern [ ] /* a work array of size n */
)
{
Entry xk ;
Entry *xp, *Lval ;
Int k, deg, *ip, j, row, *Lpos, *Lilen, *Lip, llen, lp, newLchain,
pos, npiv, n1, *Li ;
/* ---------------------------------------------------------------------- */
if (Numeric->n_row != Numeric->n_col) return (0.) ;
npiv = Numeric->npiv ;
Lpos = Numeric->Lpos ;
Lilen = Numeric->Lilen ;
Lip = Numeric->Lip ;
n1 = Numeric->n1 ;
#ifndef NDEBUG
DEBUG4 (("Lsolve start:\n")) ;
for (j = 0 ; j < Numeric->n_row ; j++)
{
DEBUG4 (("Lsolve start "ID": ", j)) ;
EDEBUG4 (X [j]) ;
DEBUG4 (("\n")) ;
}
#endif
/* ---------------------------------------------------------------------- */
/* singletons */
/* ---------------------------------------------------------------------- */
for (k = 0 ; k < n1 ; k++)
{
DEBUG4 (("Singleton k "ID"\n", k)) ;
xk = X [k] ;
deg = Lilen [k] ;
if (deg > 0 && IS_NONZERO (xk))
{
lp = Lip [k] ;
Li = (Int *) (Numeric->Memory + lp) ;
lp += UNITS (Int, deg) ;
Lval = (Entry *) (Numeric->Memory + lp) ;
for (j = 0 ; j < deg ; j++)
{
DEBUG4 ((" row "ID" k "ID" value", Li [j], k)) ;
EDEBUG4 (Lval [j]) ;
DEBUG4 (("\n")) ;
/* X [Li [j]] -= xk * Lval [j] ; */
MULT_SUB (X [Li [j]], xk, Lval [j]) ;
}
}
}
/* ---------------------------------------------------------------------- */
/* rest of L */
/* ---------------------------------------------------------------------- */
deg = 0 ;
for (k = n1 ; k < npiv ; k++)
{
/* ------------------------------------------------------------------ */
/* make column of L in Pattern [0..deg-1] */
/* ------------------------------------------------------------------ */
lp = Lip [k] ;
newLchain = (lp < 0) ;
if (newLchain)
{
lp = -lp ;
deg = 0 ;
DEBUG4 (("start of chain for column of L\n")) ;
}
/* remove pivot row */
pos = Lpos [k] ;
if (pos != EMPTY)
{
DEBUG4 ((" k "ID" removing row "ID" at position "ID"\n",
k, Pattern [pos], pos)) ;
ASSERT (!newLchain) ;
ASSERT (deg > 0) ;
ASSERT (pos >= 0 && pos < deg) ;
ASSERT (Pattern [pos] == k) ;
Pattern [pos] = Pattern [--deg] ;
}
/* concatenate the pattern */
ip = (Int *) (Numeric->Memory + lp) ;
llen = Lilen [k] ;
for (j = 0 ; j < llen ; j++)
{
row = *ip++ ;
DEBUG4 ((" row "ID" k "ID"\n", row, k)) ;
ASSERT (row > k) ;
Pattern [deg++] = row ;
}
/* ------------------------------------------------------------------ */
/* use column k of L */
/* ------------------------------------------------------------------ */
xk = X [k] ;
if (IS_NONZERO (xk))
{
xp = (Entry *) (Numeric->Memory + lp + UNITS (Int, llen)) ;
for (j = 0 ; j < deg ; j++)
{
DEBUG4 ((" row "ID" k "ID" value", Pattern [j], k)) ;
EDEBUG4 (*xp) ;
DEBUG4 (("\n")) ;
/* X [Pattern [j]] -= xk * (*xp) ; */
MULT_SUB (X [Pattern [j]], xk, *xp) ;
xp++ ;
}
}
}
#ifndef NDEBUG
for (j = 0 ; j < Numeric->n_row ; j++)
{
DEBUG4 (("Lsolve done "ID": ", j)) ;
EDEBUG4 (X [j]) ;
DEBUG4 (("\n")) ;
}
DEBUG4 (("Lsolve done.\n")) ;
#endif
return (MULTSUB_FLOPS * ((double) Numeric->lnz)) ;
}