function graph2d(f,lim,par)

% function to display contour graph of function
% input is function f, lim = [xlo xhi ylo yhi],
% and par is vector of parameters used in function
% uses a 30 by 30 grid and displays contour lines
% at .1 mode, .01 mode, and .001 mode

xlo=lim(1); xhi=lim(2); ylo=lim(3); yhi=lim(4);
npt=30;

x=linspace(xlo,xhi,npt);
y=linspace(ylo,yhi,npt);
[X,Y]=meshgrid(x,y);

Z=feval(f,[X(:) Y(:)],par);
Z=reshape(Z,npt,npt);

Z=Z-max(max(Z));
contour(x,y,Z,-6.9:2.3:0);
grid off
legend('.001 m','.01 m','.1 m')