function [Y] = ellipse_residual (X, z, a, b, alpha);%ELLIPSE_RESIDUAL       Computes the residual vector "X - ellipse"%% [Y] = ellipse_residual (X, z, a, b, alpha);% computes the residual vector "X - ellipse" in the% transformed system (rotated by -alpha).%% X: given points <X(i,1), X(i,2)>% z, a, b, alpha: ellipse parameters%% Y: residual vector "X - ellipse" for the transformed system.%    <Y(i), Y(i+m)> difference vector for i-th point (m == nofpoints)    s = sin(alpha);  c = cos(alpha);  Q = [c -s; s c];    x = [X(:,1) - z(1), X(:,2) - z(2)]*Q;  phi = ellipse_phi (x, a, b);  Y = x - [a*cos(phi), b*sin(phi)];  Y = [Y(:,1); Y(:,2)];end % ellipse_residual