Matrix for a Binomial Tree - American option

Hi everyone, i haven't a lot of experience in matlab and i have to do a project about pricing options. The problem is about the Creation of the price forecast Matrix: i have two rate, up and down, that is the market direction. The Matrix is this:

 [d^0*u^0, d^0*u^1, d^0*u^2, d^0*u^3; 
     0   , d^1*u^0, d^1*u^1, d^1*u^2; 
     0   ,    0   , d^2*u^0, d^2*u^1; 
     0   ,    0   ,    0   , d^3*u^0]

I would use two for but i don't know hot to index the columns because aren't form 0 to 3 but for every row, they change. The two index are from 0 to 3 but is just for easiness, the index are input because are the option maturity.

Beyond the financial things, my question is how to create that Matrix, i hope i was clear,

Thanks!

-- Andrea

[andreastasia]

I found a solution: i have used a toeplitz Matrix of a vector from 0 to maturity for the up exponent, and take the "triu"; for the down exponent i've used:

    for i=1:step+1
    for k=1:step+1

        X(i,k)=(i-1);

   end
   end
   down=triu(X);

Now i'll close the question, i write this if someone will have the same problem

Andrea