Q:

Matlab contourf

If I'm asked to plot a function S with "level lines" abs(S) = 0:0.1:1, how do I do that?
I looked up the solution: 
  [X,Y] = meshgrid(-15:0.1:15);
  Z = X + i*Y;
  contourf(X,Y,abs(S),[1 1]);

where they pass in the fourth argument [1 1] but I've no idea what it's doing. Why do they pass in [1 1] if they ask me for lines between 0 and 1?
Any help is much appreciated!

A:

They're making a mistake. 
The help to contourf states 

To draw a single contour of level i, use contour(Z,[i i])

So they're drawing a single contour line at 1.
You want to write
contourf(X,Y,abs(S),0:0.1:1);

because the help says

contourf(Z,v) draws a filled contour
  plot of matrix Z with contour lines at
  the data values specified in the
  monotonically increasing vector v. The
  number of contour levels is equal to
  length(v)

