/**
* LU Decomposition Back Solve; this method takes the LU matrix and the permutation vector
* produced by the GMatrix method LUD and solves the equation (LU)*x = b by placing the solution
* vector x into this vector. This vector should be the same length or longer than b.
*
* @param LU The matrix into which the lower and upper decompostions have been placed
* @param b The b vector in the equation (LU)*x = b
* @param permutation The row permuations that were necessary to produce the LU matrix parameter
*/
public final void LUDBackSolve(GMatrix LU, GVector b, GVector permutation) {
int size = LU.nRow * LU.nCol;
double[] temp = new double[size];
double[] result = new double[size];
int[] row_perm = new int[b.getSize()];
int i, j;
if (LU.nRow != b.getSize()) {
throw new MismatchedSizeException(VecMathI18N.getString("GVector16"));
}
if (LU.nRow != permutation.getSize()) {
throw new MismatchedSizeException(VecMathI18N.getString("GVector24"));
}
if (LU.nRow != LU.nCol) {
throw new MismatchedSizeException(VecMathI18N.getString("GVector25"));
}
for (i = 0; i < LU.nRow; i++) {
for (j = 0; j < LU.nCol; j++) {
temp[i * LU.nCol + j] = LU.values[i][j];
}
}
for (i = 0; i < size; i++) result[i] = 0.0;
for (i = 0; i < LU.nRow; i++) result[i * LU.nCol] = b.values[i];
for (i = 0; i < LU.nCol; i++) row_perm[i] = (int) permutation.values[i];
GMatrix.luBacksubstitution(LU.nRow, temp, row_perm, result);
for (i = 0; i < LU.nRow; i++) this.values[i] = result[i * LU.nCol];
}
