%%%%%%%%%%%%%%%%%%
% compute and plot vector field 
%%%%%%%%%%%%%%%%%%

%set up grid points
xrange=xmin:gridsizex:xmax; 
yrange=ymin:gridsizey:ymax;

%compute vector at each grid point
for nx=1:length(xrange)
 for ny=1:length(yrange)
  tempvec=linearf(0,[xrange(nx);yrange(ny)]);
  DX(ny,nx)=tempvec(1);
  DY(ny,nx)=tempvec(2);
 end
end

%plot the vector field
axis([xmin,xmax,ymin,ymax])
hold on
quiver(xrange,yrange,DX,DY,arrowlength)