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Old   August 15, 2006, 00:05
Default A problem in FORTRAN programming
  #1
Behafarid
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Hello friends. I have a problem in FORTRAN programming. I need to divide a larg zone into several parts but I can't define a matrix bigger than (4*1600*500) because the program fails and There is not any message to understand the reason of the error. I realy dont know what I have to do. PLEASE HELP ME. Thank you very much. By.
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Old   August 15, 2006, 06:27
Default Re: A problem in FORTRAN programming
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TG
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You are probably having a memory problem.

1)put the matrix into its own named common block

2)If that does not work, you might try building it as a 64bit code.
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Old   August 16, 2006, 04:52
Default Re: A problem in FORTRAN programming
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Behafarid
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Hello.

Thank you very much for your help but I didn't understand what exactly I have to do know. Please explain me more. As I asked my friends, It is a common problem in CFD programming but none of them could help me. Thank again.

Best regards. Behafarid
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Old   August 16, 2006, 06:39
Default Re: A problem in FORTRAN programming
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peter
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what is your compiler and platform and your physical memory size, i think it is not serious problem and resolved very easily.
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Old   August 16, 2006, 10:11
Default Re: A problem in FORTRAN programming
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Renato.
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First of all, let me do a simple calculation:

4*1600*500 = 3200000 coeficients

assuming double precision (8 bytes per coeficient) -- and that you're not spending more memory in other parts of your program -- you'll need

3200000 * 8 = 25600000 Bytes

or about 24.4 MBytes

(if I'm not wrong in my calc) It doesn't seem to be hard allocate such array.

Is this array inside a subroutine? You can be running into stack size problems.

Have you tried to allocate this array statically or dynamically?

Regards

Renato.

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Old   August 16, 2006, 11:09
Default Re: A problem in FORTRAN programming
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Steve
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Your problem is almost certainly stack size related. If you delare a variable inside a function, it'll use stack memory unless forced to use heap. To make it use heap memory, make it static. (e.g. in a COMMON block, defined in a DATA statement).
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Old   August 16, 2006, 12:16
Default Re: A problem in FORTRAN programming
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Renato.
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Try the following examples (using Fortran 90 sintax)

program foo real*8, allocatable :: a( n = 4*1600*500 allocate(a(n)) call SomeRoutine(a,n) deallocate(a) end program

subroutine SomeRoutine(a,n) ! You must avoid the use of the array size here. It always causes stack problems real*8 :: a(1) ... end subroutine

! --- END OF THE FIRST EXAMPLE ---

The same thing could be done with modules

module SomeData real*8, allocatable :: a( end module SomeData

program foo use SomeData n = 4*1600*500 allocate(a(n)) call SomeRoutine deallocate(a) end program

subroutine SomeRoutine use SomeData ... end subroutine

! --- END OF THE SECOND EXAMPLE ---

Here the array "a" is made accessible through the use of the module

Good lucky ;o)

Renato.

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