SparseLU_column_bmod.h

// 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>
// Copyright (C) 2012 Gael Guennebaud <gael.guennebaud@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 xcolumn_bmod.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_COLUMN_BMOD_H
#define SPARSELU_COLUMN_BMOD_H

// IWYU pragma: private
#include "./InternalHeaderCheck.h"

namespace Eigen {

namespace internal {
template <typename Scalar, typename StorageIndex>
Index SparseLUImpl<Scalar, StorageIndex>::column_bmod(const Index jcol, const Index nseg, BlockScalarVector dense,
                                                      ScalarVector& tempv, BlockIndexVector segrep,
                                                      BlockIndexVector repfnz, Index fpanelc, GlobalLU_t& glu) {
  Index jsupno, k, ksub, krep, ksupno;
  Index lptr, nrow, isub, irow, nextlu, new_next, ufirst;
  Index fsupc, nsupc, nsupr, luptr, kfnz, no_zeros;
  /* krep = representative of current k-th supernode
   * fsupc =  first supernodal column
   * nsupc = number of columns in a supernode
   * nsupr = number of rows in a supernode
   * luptr = location of supernodal LU-block in storage
   * kfnz = first nonz in the k-th supernodal segment
   * no_zeros = no lf leading zeros in a supernodal U-segment
   */

  jsupno = glu.supno(jcol);
  // For each nonzero supernode segment of U[*,j] in topological order
  k = nseg - 1;
  Index d_fsupc;  // distance between the first column of the current panel and the
                  // first column of the current snode
  Index fst_col;  // First column within small LU update
  Index segsize;
  for (ksub = 0; ksub < nseg; ksub++) {
    krep = segrep(k);
    k--;
    ksupno = glu.supno(krep);
    if (jsupno != ksupno) {
      // outside the rectangular supernode
      fsupc = glu.xsup(ksupno);
      fst_col = (std::max)(fsupc, fpanelc);

      // Distance from the current supernode to the current panel;
      // d_fsupc = 0 if fsupc > fpanelc
      d_fsupc = fst_col - fsupc;

      luptr = glu.xlusup(fst_col) + d_fsupc;
      lptr = glu.xlsub(fsupc) + d_fsupc;

      kfnz = repfnz(krep);
      kfnz = (std::max)(kfnz, fpanelc);

      segsize = krep - kfnz + 1;
      nsupc = krep - fst_col + 1;
      nsupr = glu.xlsub(fsupc + 1) - glu.xlsub(fsupc);
      nrow = nsupr - d_fsupc - nsupc;
      Index lda = glu.xlusup(fst_col + 1) - glu.xlusup(fst_col);

      // Perform a triangular solver and block update,
      // then scatter the result of sup-col update to dense
      no_zeros = kfnz - fst_col;
      if (segsize == 1)
        LU_kernel_bmod<1>::run(segsize, dense, tempv, glu.lusup, luptr, lda, nrow, glu.lsub, lptr, no_zeros);
      else
        LU_kernel_bmod<Dynamic>::run(segsize, dense, tempv, glu.lusup, luptr, lda, nrow, glu.lsub, lptr, no_zeros);
    }  // end if jsupno
  }    // end for each segment

  // Process the supernodal portion of  L\U[*,j]
  nextlu = glu.xlusup(jcol);
  fsupc = glu.xsup(jsupno);

  // copy the SPA dense into L\U[*,j]
  Index mem;
  new_next = nextlu + glu.xlsub(fsupc + 1) - glu.xlsub(fsupc);
  Index offset = internal::first_multiple<Index>(new_next, internal::packet_traits<Scalar>::size) - new_next;
  if (offset) new_next += offset;
  while (new_next > glu.nzlumax) {
    mem = memXpand<ScalarVector>(glu.lusup, glu.nzlumax, nextlu, LUSUP, glu.num_expansions);
    if (mem) return mem;
  }

  for (isub = glu.xlsub(fsupc); isub < glu.xlsub(fsupc + 1); isub++) {
    irow = glu.lsub(isub);
    glu.lusup(nextlu) = dense(irow);
    dense(irow) = Scalar(0.0);
    ++nextlu;
  }

  if (offset) {
    glu.lusup.segment(nextlu, offset).setZero();
    nextlu += offset;
  }
  glu.xlusup(jcol + 1) = StorageIndex(nextlu);  // close L\U(*,jcol);

  /* For more updates within the panel (also within the current supernode),
   * should start from the first column of the panel, or the first column
   * of the supernode, whichever is bigger. There are two cases:
   *  1) fsupc < fpanelc, then fst_col <-- fpanelc
   *  2) fsupc >= fpanelc, then fst_col <-- fsupc
   */
  fst_col = (std::max)(fsupc, fpanelc);

  if (fst_col < jcol) {
    // Distance between the current supernode and the current panel
    // d_fsupc = 0 if fsupc >= fpanelc
    d_fsupc = fst_col - fsupc;

    lptr = glu.xlsub(fsupc) + d_fsupc;
    luptr = glu.xlusup(fst_col) + d_fsupc;
    nsupr = glu.xlsub(fsupc + 1) - glu.xlsub(fsupc);  // leading dimension
    nsupc = jcol - fst_col;                           // excluding jcol
    nrow = nsupr - d_fsupc - nsupc;

    // points to the beginning of jcol in snode L\U(jsupno)
    ufirst = glu.xlusup(jcol) + d_fsupc;
    Index lda = glu.xlusup(jcol + 1) - glu.xlusup(jcol);
    MappedMatrixBlock A(&(glu.lusup.data()[luptr]), nsupc, nsupc, OuterStride<>(lda));
    VectorBlock<ScalarVector> u(glu.lusup, ufirst, nsupc);
    u = A.template triangularView<UnitLower>().solve(u);

    new (&A) MappedMatrixBlock(&(glu.lusup.data()[luptr + nsupc]), nrow, nsupc, OuterStride<>(lda));
    VectorBlock<ScalarVector> l(glu.lusup, ufirst + nsupc, nrow);
    l.noalias() -= A * u;

  }  // End if fst_col
  return 0;
}

}  // end namespace internal
}  // end namespace Eigen

#endif  // SPARSELU_COLUMN_BMOD_H