Hi it is me again!

This is a programming question, do you know how to define a vector that could give you the value of a variable calculated one iteration before. In posdat.f, this could mean a variable 'A' that gives you the value of variable 'B' calculated on the past level. For example you calculate B as a function of the mass fraction of scalar 1: B=t(ic,2)*alpha, and you would like to know what this value was the last time it was calculated: A=B(past), not this level or itteration the "past one".

Many thanks CM

In each iteration you calculate B and then set A=B. As long as A is either SAVEd or it is in a COMMON block, it will be "remembered" in the next iteration (up until the point when you do A=B anyway).