how to plot this 2D function

I'm trying to solve this 2D problem in matlab,

for a given matrices (2*2 dimension for example)

sigma=the maximum singular value of matrix K;

the fist axix is p and the secon axix is s where 1<p<4 and 1<s<4 and

K=[p-1 -2; -3 s-4]

how to plot the surf that represnt for each pair (p,s) the ( sigma=the maximum singular value of matrix K) like this graph ( note that this graph is for a nother example ),

[SALAH ALRABEEI]

assum F is your matrix of size n×m where n and m are length of s and p.

     surf(s,p,F)

[Lewis Fer]

and how to compute thes igma=the maximum singular value of matrix K with the plot ?