How to write matlab code for this algorithm

Hi all!! I Don't have any idea, how to write the 4th step in matlab.can anyone help me to solve this. I'm attaching the algorithm for your reference.

[KALYAN ACHARJYA]

What are the f1,f2,f3 and f4?

[Rik]

Have a read here and here. It will greatly improve your chances of getting an answer. You can find guidelines for posting homework on this forum here.

[Rocky]

f1,f2,f3,f4 are constant values.@ kalyan. The 4 th step implies f(x,y).Instead of x,y here they are given s and t.My doubt

is how to write this form in matlab.I tried diff(f1,s1,t1),butIt doesnt give correct answer.

[Rocky]

Thanks Rik..I'll see the guidelines.@Rik