GeneralMatrix dRx = new GeneralMatrix(3 * getMappedPositions().size(), 1);
for (int i = 0; i < x.getNumRow(); i = i + 3) {
GeneralMatrix subMatrix = new GeneralMatrix(3, 1);
x.copySubMatrix(i, 0, 3, 1, 0, 0, subMatrix);
subMatrix.sub(R, subMatrix);
subMatrix.copySubMatrix(0, 0, 3, 1, i, 0, dRx);
}
return dRx;
}