Not able to use previous element in matrix inside for loop

I am trying to figure out why the following simple code doesnt work:

sigma=nan(size(returns,1),1);

sigma(1)=0;

sigma(2)=0;

sigma(3)=R_p(2,1)^2;

for j=4:size(returns,1)

sigma(j)=0.94*(sigma((j-1)))^2+(1-0.94)*(R_p(j-1))^2;

end

It returns the sigma matrix with "inf" as elements. Anybody who knows why?What am i missing?

[Bhaskar R]

What is R_p value?

Answer 1

[Muhammad Usama Sharaf SAAFI]

Declare R_p in above code. You are not showng complete code here.