function h=ellipse(ra,rb,ang,x0,y0,C,Nb)
% Ellipse adds ellipses to the current plot
%
% ELLIPSE(ra,rb,ang,x0,y0) adds an ellipse with semimajor axis of ra,
% a semimajor axis of radius rb, a semimajor axis of ang, centered at
% the point x0,y0.
%
% The length of ra, rb, and ang should be the same.
% If ra is a vector of length L and x0,y0 scalars, L ellipses
% are added at point x0,y0.
% If ra is a scalar and x0,y0 vectors of length M, M ellipse are with the same
% radii are added at the points x0,y0.
% If ra, x0, y0 are vectors of the same length L=M, M ellipses are added.
% If ra is a vector of length L and x0, y0 are vectors of length
% M~=L, L*M ellipses are added, at each point x0,y0, L ellipses of radius ra.
%
% ELLIPSE(ra,rb,ang,x0,y0,C)
% adds ellipses of color C. C may be a string ('r','b',...) or the RGB value.
% If no color is specified, it makes automatic use of the colors specified by
% the axes ColorOrder property. For several circles C may be a vector.
%
% ELLIPSE(ra,rb,ang,x0,y0,C,Nb), Nb specifies the number of points
% used to draw the ellipse. The default value is 300. Nb may be used
% for each ellipse individually.
%
% h=ELLIPSE(...) returns the handles to the ellipses.
%
% as a sample of how ellipse works, the following produces a red ellipse
% tipped up at a 45 deg axis from the x axis
% ellipse(1,2,pi/8,1,1,'r')
%
% note that if ra=rb, ELLIPSE plots a circle
%
% written by D.G. Long, Brigham Young University, based on the
% CIRCLES.m original
% written by Peter Blattner, Institute of Microtechnology, University of
% Neuchatel, Switzerland, blattner@imt.unine.ch
% Check the number of input arguments
if nargin<1,
ra=[];
end;
if nargin<2,
rb=[];
end;
if nargin<3,
ang=[];
end;
%if nargin==1,
% error('Not enough arguments');
%end;
if nargin<5,
x0=[];
y0=[];
end;
if nargin<6,
C=[];
end
if nargin<7,
Nb=[];
end
% set up the default values
if isempty(ra),ra=1;end;
if isempty(rb),rb=1;end;
if isempty(ang),ang=0;end;
if isempty(x0),x0=0;end;
if isempty(y0),y0=0;end;
if isempty(Nb),Nb=300;end;
if isempty(C),C=get(gca,'colororder');end;
% work on the variable sizes
x0=x0(:);
y0=y0(:);
ra=ra(:);
rb=rb(:);
ang=ang(:);
Nb=Nb(:);
if isstr(C),C=C(:);end;
if length(ra)~=length(rb),
error('length(ra)~=length(rb)');
end;
if length(x0)~=length(y0),
error('length(x0)~=length(y0)');
end;
% how many inscribed elllipses are plotted
if length(ra)~=length(x0)
maxk=length(ra)*length(x0);
else
maxk=length(ra);
end;
% drawing loop
for k=1:maxk
if length(x0)==1
xpos=x0;
ypos=y0;
radm=ra(k);
radn=rb(k);
if length(ang)==1
an=ang;
else
an=ang(k);
end;
elseif length(ra)==1
xpos=x0(k);
ypos=y0(k);
radm=ra;
radn=rb;
an=ang;
elseif length(x0)==length(ra)
xpos=x0(k);
ypos=y0(k);
radm=ra(k);
radn=rb(k);
an=ang(k)
else
rada=ra(fix((k-1)/size(x0,1))+1);
radb=rb(fix((k-1)/size(x0,1))+1);
an=ang(fix((k-1)/size(x0,1))+1);
xpos=x0(rem(k-1,size(x0,1))+1);
ypos=y0(rem(k-1,size(y0,1))+1);
end;
co=cos(an);
si=sin(an);
the=linspace(0,2*pi,Nb(rem(k-1,size(Nb,1))+1,:)+1);
% x=radm*cos(the)*co-si*radn*sin(the)+xpos;
% y=radm*cos(the)*si+co*radn*sin(the)+ypos;
h(k)=line(radm*cos(the)*co-si*radn*sin(the)+xpos,radm*cos(the)*si+co*radn*sin(the)+ypos);
set(h(k),'color',C(rem(k-1,size(C,1))+1,:));
end;