Hello,

So I want to create an image of the cusp catastrophe that looks like this 

but instead I have been getting this image where the discontinuity is plotted out to infinity

I have tried to split up the surfaces on either side of this but I haven't been able to display both on the same plot whilst using implicitplot3d. 
This is the line of code for the image, there't not much too it
"
with(plots);

implicitplot3d(x^4+x^2*z+x*y, x = -7 .. 7, y = -50 .. 50, z = -10 .. 5, axes = boxed, style = surfacecontour, grid = [60, 60, 60], orientation = [180, 8, 175], 'transparency' = .1);
"
If anyone could help or point me in the right direction that would be great.
Cheers,
Darryl A.M.