Hi All. I have parallel PDE/CFD code in fortran. Let we consider it consisting of two parts:
1) Startup part; that includes input reads, splits, distributions, forming neighborhood information arrays, grid arrays, and all related. It includes most of the necessary array declarations. 2) Iterative part; we proceed the solution in time. Approach One: ============ What I do is that during the Startup phase, I declare the most array allocatable and then allocate them sizes depending upon the input reads and domain partitioning. And then In the iterative phase I utilize those arrays. But I "do not" allocate/deallocate new arrays in the iterative part. Approach Two: ============ I think that, what if I first use to run only the start -up phase of my parallel code having allocatable like things and get the sizes-values required for array allocations for a specific problem size and partitioning. Then I use these values as constant in another version of my code in which I will declare array with the constant values obtained. So my question is that will there be any significant performance/efficiency difference in the "ITERATIVE part" if the approach two is used (having arrays declared fixed sizes/values)? -------------------- ANOTHER QUESTION ABOUT CALLING SUBROUTINES: Assume two ways: 1) One way is that we declare arrays in some global module and "USE" arrays in subroutines which ever is needed there. 2) We pass a large number of arrays (10, 20 or 30 may be) in the header while making call to a subroutine. Which way is quite fast and efficient over the other? Thank You for your kind attention. with best regards, Amjad Ali.
