function [majrax,majaz,minrax,minaz,elptcty]=pcaben(u,v)
% Principal components of 2-d (e.g. current meter) data
%
%Called by elpspam.m to calculate ellipse parameters - B.G. 2000
%
%Inputs:  u and v (eastward and northward current velocities)
%
%outputs: major axis (majrax)	minor axis (minrax)
%			 major azimuth (majaz) minor azimuth (minaz)
%			 elipticity (elptcty)
%
% function pca(u,v,[[s],ipost])
%
% u and v are column vectors with x and y data
% s is an optional length for the axes
% ipost is an optional flag 0=no action, 1=plot input data
%
% Chris Sherwood, USGS
% March 17, 1999
%
% Modified by jpx on 6-14-99 to be used in CMGTooL
% Modified by jpx on 10-14-99 to plot ellipses
% 2/16/2000 modified by Ben Gutierrez to incorporate into LTM work.
% -ipost and [s] no longer necessary to this rountine which is based on PCA.M which is included in
% CMGTool.
% 
mu = mean(u);
mv = mean(v);
C = cov(u,v);
[V,D] = eig(C);

x1 = [.5*sqrt(D(1,1))*V(1,1);-.5*sqrt(D(1,1))*V(1,1)];
y1 = [.5*sqrt(D(1,1))*V(2,1);-.5*sqrt(D(1,1))*V(2,1)];
x2 = [.5*sqrt(D(2,2))*V(1,2);-.5*sqrt(D(2,2))*V(1,2)];
y2 = [.5*sqrt(D(2,2))*V(2,2);-.5*sqrt(D(2,2))*V(2,2)];
[mspd mdir]=pcoord( mu, mv );

for i=1:2
	eval(['[ leng(i), az(i) ] = pcoord( x' num2str(i) '(1), y' num2str(i) '(1) );']);
end;

if leng(1)>=leng(2)
	majr=leng(1);majaz=az(1);
	minr=leng(2);minaz=az(2);
else
	majr=leng(2);majaz=az(2);
	minr=leng(1);minaz=az(1);
end;


majrax = majr*2;
minrax = minr*2;
elptcty = (1 - minr/majr);