double alignStep(final RandomAccessibleInterval<T> image) {
// compute error image = warped image - template
computeDifference(Views.extendBorder(image), currentTransform, template, error);
// compute transform parameter update
final double[] gradient = new double[numParameters];
for (int p = 0; p < numParameters; ++p) {
final Cursor<T> err = Views.flatIterable(error).cursor();
for (final T t : Views.flatIterable(Views.hyperSlice(descent, n, p)))
gradient[p] += t.getRealDouble() * err.next().getRealDouble();
}
final double[] dp = new double[numParameters];
LinAlgHelpers.mult(Hinv, gradient, dp);
// udpate transform
currentTransform.preConcatenate(warpFunction.getAffine(dp));
// return norm of parameter update vector
return LinAlgHelpers.length(dp);
}
