src/sim/linear_solver.cc

   1 /*
   2  * Copyright (c) 2015 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
  18  * redistributions in binary form must reproduce the above copyright
  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  31  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  */
  37
  38 #include "sim/linear_solver.hh"
  39
  40 std::vector <double>
  41 LinearSystem::solve() const
  42 {
  43     // Solve using gauss elimination, not ideal for big matrices
  44     std::vector < LinearEquation > smatrix = this->matrix;
  45
  46     unsigned order = smatrix.size();
  47     for (unsigned row = 0; row < order - 1; row++) {
  48         // Look for a non-zero row, and swap
  49         for (unsigned i = row; i < order; i++) {
  50             if (smatrix[i][row] != 0.0f) {
  51                 if (i != row) {
  52                     LinearEquation tmp = smatrix[i];
  53                     smatrix[i] = smatrix[row];
  54                     smatrix[row] = tmp;
  55                 }
  56                 break;
  57             }
  58         }
  59
  60         // Divide row by leading number to make it 1.0
  61         smatrix[row] *= (1.0f / smatrix[row][row]);
  62
  63         // Add it (properly scaled) to the rows below
  64         for (unsigned i = row + 1; i < order; i++) {
  65             LinearEquation t = smatrix[row];
  66             t *= -1.0f * smatrix[i][row];
  67             smatrix[i] = smatrix[i] + t;
  68         }
  69     }
  70
  71     // smatrix is now a triangular matrix with diagonal being 1
  72     // Just backproagate variable values from order-1 till 0
  73     std::vector <double> ret(order, 0.0f);
  74     for (int row = order - 1; row >= 0; row--) {
  75         // Unknown value
  76         ret[row] = -smatrix[row][smatrix[row].cnt()] / smatrix[row][row];
  77         // Propagate variable in the cnt term
  78         for (int i = row - 1; i >= 0; i--) {
  79             smatrix[i][smatrix[i].cnt()] += ret[row] * smatrix[i][row];
  80             smatrix[i][row] = 0.0f;
  81         }
  82     }
  83
  84     return ret;
  85 }