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linear_solver.cc
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37  * Authors: David Guillen Fandos
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39 
40 #include "sim/linear_solver.hh"
41 
44 {
45  // Solve using gauss elimination, not ideal for big matrices
46  std::vector < LinearEquation > smatrix = this->matrix;
47 
48  unsigned order = smatrix.size();
49  for (unsigned row = 0; row < order - 1; row++) {
50  // Look for a non-zero row, and swap
51  for (unsigned i = row; i < order; i++) {
52  if (smatrix[i][row] != 0.0f) {
53  if (i != row) {
54  LinearEquation tmp = smatrix[i];
55  smatrix[i] = smatrix[row];
56  smatrix[row] = tmp;
57  }
58  break;
59  }
60  }
61 
62  // Divide row by leading number to make it 1.0
63  smatrix[row] *= (1.0f / smatrix[row][row]);
64 
65  // Add it (properly scaled) to the rows below
66  for (unsigned i = row + 1; i < order; i++) {
67  LinearEquation t = smatrix[row];
68  t *= -1.0f * smatrix[i][row];
69  smatrix[i] = smatrix[i] + t;
70  }
71  }
72 
73  // smatrix is now a triangular matrix with diagonal being 1
74  // Just backproagate variable values from order-1 till 0
75  std::vector <double> ret(order, 0.0f);
76  for (int row = order - 1; row >= 0; row--) {
77  // Unknown value
78  ret[row] = -smatrix[row][smatrix[row].cnt()] / smatrix[row][row];
79  // Propagate variable in the cnt term
80  for (int i = row - 1; i >= 0; i--) {
81  smatrix[i][smatrix[i].cnt()] += ret[row] * smatrix[i][row];
82  smatrix[i][row] = 0.0f;
83  }
84  }
85 
86  return ret;
87 }
std::vector< double > solve() const
Bitfield< 7 > i
Definition: miscregs.hh:1378
Bitfield< 6 > f
Definition: miscregs.hh:1379
std::vector< LinearEquation > matrix
This class describes a linear equation with constant coefficients.
Bitfield< 5 > t
Definition: miscregs.hh:1382

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