first of all, sorry about this lame question but I’m totally noob … so, my problem is:

how to declare an time and time variation (delta time) indexed variable, like

p(t,n)= A(n)+B(n)X(t)

which is a linear equation for pricing a zero-coupon (default free) bond at time “t” that pays 1 at time “t+n”. the major problem is that when you advance to “t+1” “n” becomes “n-1”…