/**
* Computes inverse coefficients
*
* @param border
* @param forward Forward coefficients.
* @param inverse Inverse used in the inner portion of the data stream.
* @return
*/
private static WlBorderCoef<WlCoef_F32> computeBorderCoefficients(
BorderIndex1D border, WlCoef_F32 forward, WlCoef_F32 inverse) {
int N = Math.max(forward.getScalingLength(), forward.getWaveletLength());
N += N % 2;
N *= 2;
border.setLength(N);
// Because the wavelet transform is a linear invertible system the inverse coefficients
// can be found by creating a matrix and inverting the matrix. Boundary conditions are then
// extracted from this inverted matrix.
DenseMatrix64F A = new DenseMatrix64F(N, N);
for (int i = 0; i < N; i += 2) {
for (int j = 0; j < forward.scaling.length; j++) {
int index = border.getIndex(j + i + forward.offsetScaling);
A.add(i, index, forward.scaling[j]);
}
for (int j = 0; j < forward.wavelet.length; j++) {
int index = border.getIndex(j + i + forward.offsetWavelet);
A.add(i + 1, index, forward.wavelet[j]);
}
}
LinearSolver<DenseMatrix64F> solver = LinearSolverFactory.linear(N);
if (!solver.setA(A) || solver.quality() < 1e-5) {
throw new IllegalArgumentException("Can't invert matrix");
}
DenseMatrix64F A_inv = new DenseMatrix64F(N, N);
solver.invert(A_inv);
int numBorder = UtilWavelet.borderForwardLower(inverse) / 2;
WlBorderCoefFixed<WlCoef_F32> ret = new WlBorderCoefFixed<>(numBorder, numBorder + 1);
ret.setInnerCoef(inverse);
// add the lower coefficients first
for (int i = 0; i < ret.getLowerLength(); i++) {
computeLowerCoef(inverse, A_inv, ret, i * 2);
}
// add upper coefficients
for (int i = 0; i < ret.getUpperLength(); i++) {
computeUpperCoef(inverse, N, A_inv, ret, i * 2);
}
return ret;
}
