[Beowulf] Array Declaration approach difference

amjad ali amjad11 at gmail.com
Sat Nov 14 06:47:07 PST 2009

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 contant in another version of my code in which I
will declare array with the contant values obtained.

So my question is that will there be any significant performance/efficiency
diffrence in the "ITERATIVE part" if the approch two is used (having arrays
declared fixed sizes/values)?

Thank You for your kind attention.

with best regards,
Amjad Ali.
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