function [a, b, theta] = sym2par(A)

% [a, b, theta] = sym2par(A)
%
% DESC:
% computes the semiaxis a, b and rotation angle theta of the ellipse
% represented by the symmetric matrix A
%
% AUTHOR
% Marco Zuliani - zuliani@ece.ucsb.edu
%
% VERSION:
% 1.0
%
% INPUT:
% A                 = symmteric matrix such that x'*A*x
%
% OUTPUT:
% a, b              = ellipse semiaxis
% theta             = rotation angle (counterclock-wise)

[V D] = svd(A);
a = 1/sqrt(D(1,1));
b = 1/sqrt(D(2,2));
theta = atan2(V(2,1), V(1,1));

return

Published with MATLAB® 7.4