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/*
* Copyright (c) 2015 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: David Guillen Fandos
*/
#include "sim/linear_solver.hh"
std::vector <double>
LinearSystem::solve() const
{
// Solve using gauss elimination, not ideal for big matrices
std::vector < LinearEquation > smatrix = this->matrix;
unsigned order = smatrix.size();
for (unsigned row = 0; row < order - 1; row++) {
// Look for a non-zero row, and swap
for (unsigned i = row; i < order; i++) {
if (smatrix[i][row] != 0.0f) {
if (i != row) {
LinearEquation tmp = smatrix[i];
smatrix[i] = smatrix[row];
smatrix[row] = tmp;
}
break;
}
}
// Divide row by leading number to make it 1.0
smatrix[row] *= (1.0f / smatrix[row][row]);
// Add it (properly scaled) to the rows below
for (unsigned i = row + 1; i < order; i++) {
LinearEquation t = smatrix[row];
t *= -1.0f * smatrix[i][row];
smatrix[i] = smatrix[i] + t;
}
}
// smatrix is now a triangular matrix with diagonal being 1
// Just backproagate variable values from order-1 till 0
std::vector <double> ret(order, 0.0f);
for (int row = order - 1; row >= 0; row--) {
// Unknown value
ret[row] = -smatrix[row][smatrix[row].cnt()] / smatrix[row][row];
// Propagate variable in the cnt term
for (int i = row - 1; i >= 0; i--) {
smatrix[i][smatrix[i].cnt()] += ret[row] * smatrix[i][row];
smatrix[i][row] = 0.0f;
}
}
return ret;
}
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