% A script to  plot vector fields of 2 dim continuous systems
%
% The system is of the form x' = f(x)
%
% The function "f" is defined in a file called "rhs.m"
%

resolution = 10; % increase this for more arrows


global RHSNAME;
disp('Vector field generator');

setrhs;

xrange = input('Please enter the x range [0 1] -> ');
n = length(xrange);
if (n > 2), xrange = xrange(1:2); end;
if (n == 1), xrange(2) = xrange(1)+1; end;
if (n == 0), xrange = [ 0 1]; end;

yrange = input('Please enter the y range [0 1] -> '); 
n = length(yrange);
if (n > 2), yrange = yrange(1:2); end;
if (n == 1), yrange(2) = yrange(1)+1; end;
if (n == 0), yrange = [ 0 1]; end; 

disp('Working.');

dx = xrange(2)-xrange(1);
dy = yrange(2)-yrange(1);


xlist = [xrange(1) : dx/10 :  xrange(2) ];
ylist = [yrange(1) : dy/10 :  yrange(2) ];

nx = length(xlist);
ny = length(ylist);
 
dx = zeros(nx,ny);
dy = zeros(nx,ny);
 
for ii=1:nx, for jj=1:ny
        xx = [xlist(ii);ylist(jj)];
        yy = feval(RHSNAME,xx);
        dx(ii,jj) = yy(1);
        dy(ii,jj) = yy(2);
end;end;
 


disp('Done! Plotting graph.');

quiver(xlist,ylist,dx',dy');
axis([ xrange(1) , xrange(2), yrange(1), yrange(2)]);
axis('normal');