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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;