% This function mfile slices the graph of f with a plane parallel to
% xz plane. It assumes that the function f has already been graphed
% over the rectangle [a,b]\times [c,d]. The call is yslice(f,x0,y)
% when f is given as an inline function, and yslice('f',x0,y) when
% f is given in an mfile. x0 is the constant x value, and y
% is the vector of y coordinates which ranges from c to d.
function out = yslice(f, x0, y)
z = feval(f, x0, y);
high = max([z+1 0]);
low = min([z-1,0]);
c = min(y); d = max(y);
xedge = [x0 x0 x0 x0 x0];
yedge = [c d d c c];
zedge = [low low high high low];
fill3(xedge, yedge, zedge, 'b')