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.
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
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
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?