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 iterative part.
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,