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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2012 Désiré Nuentsa-Wakam <desire.nuentsa_wakam@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
/*
* NOTE: This file is the modified version of xpivotL.c file in SuperLU
* -- SuperLU routine (version 3.0) --
* Univ. of California Berkeley, Xerox Palo Alto Research Center,
* and Lawrence Berkeley National Lab.
* October 15, 2003
*
* Copyright (c) 1994 by Xerox Corporation. All rights reserved.
*
* THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY
* EXPRESSED OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
*
* Permission is hereby granted to use or copy this program for any
* purpose, provided the above notices are retained on all copies.
* Permission to modify the code and to distribute modified code is
* granted, provided the above notices are retained, and a notice that
* the code was modified is included with the above copyright notice.
*/
#ifndef SPARSELU_PIVOTL_H
#define SPARSELU_PIVOTL_H
/**
* \brief Performs the numerical pivotin on the current column of L, and the CDIV operation.
*
* Pivot policy :
* (1) Compute thresh = u * max_(i>=j) abs(A_ij);
* (2) IF user specifies pivot row k and abs(A_kj) >= thresh THEN
* pivot row = k;
* ELSE IF abs(A_jj) >= thresh THEN
* pivot row = j;
* ELSE
* pivot row = m;
*
* Note: If you absolutely want to use a given pivot order, then set u=0.0.
*
* \param jcol The current column of L
* \param u diagonal pivoting threshold
* \param [in,out]perm_r Row permutation (threshold pivoting)
* \param [in] iperm_c column permutation - used to finf diagonal of Pc*A*Pc'
* \param [out]pivrow The pivot row
* \param glu Global LU data
* \return 0 if success, i > 0 if U(i,i) is exactly zero
*
*/
template <typename Scalar, typename Index>
int SparseLUBase<Scalar,Index>::LU_pivotL(const int jcol, const RealScalar diagpivotthresh, IndexVector& perm_r, IndexVector& iperm_c, int& pivrow, GlobalLU_t& glu)
{
Index fsupc = (glu.xsup)((glu.supno)(jcol)); // First column in the supernode containing the column jcol
Index nsupc = jcol - fsupc; // Number of columns in the supernode portion, excluding jcol; nsupc >=0
Index lptr = glu.xlsub(fsupc); // pointer to the starting location of the row subscripts for this supernode portion
Index nsupr = glu.xlsub(fsupc+1) - lptr; // Number of rows in the supernode
Scalar* lu_sup_ptr = &(glu.lusup.data()[glu.xlusup(fsupc)]); // Start of the current supernode
Scalar* lu_col_ptr = &(glu.lusup.data()[glu.xlusup(jcol)]); // Start of jcol in the supernode
Index* lsub_ptr = &(glu.lsub.data()[lptr]); // Start of row indices of the supernode
// Determine the largest abs numerical value for partial pivoting
Index diagind = iperm_c(jcol); // diagonal index
RealScalar pivmax = 0.0;
Index pivptr = nsupc;
Index diag = IND_EMPTY;
RealScalar rtemp;
Index isub, icol, itemp, k;
for (isub = nsupc; isub < nsupr; ++isub) {
rtemp = std::abs(lu_col_ptr[isub]);
if (rtemp > pivmax) {
pivmax = rtemp;
pivptr = isub;
}
if (lsub_ptr[isub] == diagind) diag = isub;
}
// Test for singularity
if ( pivmax == 0.0 ) {
pivrow = lsub_ptr[pivptr];
perm_r(pivrow) = jcol;
return (jcol+1);
}
RealScalar thresh = diagpivotthresh * pivmax;
// Choose appropriate pivotal element
{
// Test if the diagonal element can be used as a pivot (given the threshold value)
if (diag >= 0 )
{
// Diagonal element exists
rtemp = std::abs(lu_col_ptr[diag]);
if (rtemp != 0.0 && rtemp >= thresh) pivptr = diag;
}
pivrow = lsub_ptr[pivptr];
}
// Record pivot row
perm_r(pivrow) = jcol;
// Interchange row subscripts
if (pivptr != nsupc )
{
std::swap( lsub_ptr[pivptr], lsub_ptr[nsupc] );
// Interchange numerical values as well, for the two rows in the whole snode
// such that L is indexed the same way as A
for (icol = 0; icol <= nsupc; icol++)
{
itemp = pivptr + icol * nsupr;
std::swap(lu_sup_ptr[itemp], lu_sup_ptr[nsupc + icol * nsupr]);
}
}
// cdiv operations
Scalar temp = Scalar(1.0) / lu_col_ptr[nsupc];
for (k = nsupc+1; k < nsupr; k++)
lu_col_ptr[k] *= temp;
return 0;
}
#endif
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