Hi all, I have discretized my equations in a way that for example the velocity depends on the velocity of the previous neighboring element so: h = number of elements t = 0: 0.5 : 10 for j= 1 : length(t) for i = 2: h v(i,j) = v(i-1,j) + b p(i,j) = p(i,j) +b end end This is not my actual formulations(codes) but the idea is that I need the value of the variable at the previous element so I start my loop from 2 to avoid getting i=0. But then this means that I don't have any values when I have i = 1 in the code. Is the only way to deal with this using boundary conditions. For example setting the value of the variable at i = 1 to be equal to that at i =2 ? I hope I am clear enough. Thanks.