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Fortran syntax help needed

Posted on 2002-06-29
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Last Modified: 2013-11-08
Trying to convert some Fortran to VB.  Here is a start of Fortran sub:

     SUBROUTINE TRIDAG(AAA,AAB,AAC,ABB,E1,NN,BCT,BCB)

     REAL*8 AAA(*),AAB(*),AAC(*),ABB(*),E1(20000)
     REAL*8 BET, GAM(20000)
     INTEGER BCT, BCB, NN
...

I thought argument AAA is an array, this also shows it is used as array:
     BET=AAB(I)-AAA(I)*GAM(I)

But, when sub is called, it seems only ONE ELEMENT is passed, instead of array:

      CALL TRIDAG(AA(1),AB(1),AC(1),BB(1),E1,NN,BCT,BCB)

     CALL TRIDAG(AA(2),AB(2),AC(2),BB(2),E1,NN,BCT,BCB)

Please, help me understand syntax ... maybe only subset of array AA is being passed?

Thanks
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Question by:ameba
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bruintje earned 400 total points
ID: 7119200
Hi ameba,

sorry that i haven't any better idea then a download, there are two trials there, you showed only part of it but i guess there's more

http://www.winsite.com/bin/Search?id=2573

maybe it could help you going until the fortran people are lurking into this

HAGD:O)Bruintje
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by:ameba
ID: 7119218
Thanks, Bruintje

I expect converter would convert it to:

Private Sub TRIDAG(AAA() As Double, AAB() As Double, AAC() As Double, ABB() As Double, _
     E1() As Double, NN As Long, BCT As Long, BCB As Long)

and the call to:
     CALL TRIDAG(AA(1), AB(1), AC(1), BB(1), E1, NN, BCT, BCB)

and I would get error "Expecting array" with "AA(1)" highlighted.
I'll try it later, if there isn't any 'easier' suggestion.
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by:ameba
ID: 7119366
I tested "Convert Fortran to Visual Basic" but it doesn't recognize declaration.
Dim aaa(*)  as double   ' this doesn't work in VB

I don't see many Fortran programmers on EE  :-)
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LVL 15

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by:ameba
ID: 7119434
AAA(*)
is 'Assumed-size array', its size is known to caller
http://www.ibiblio.org/pub/languages/fortran/ch2-4.html

Call Tridag(AA(2), ...)
I think this means we are passing array block, starting with element 2.  Will try and see if I get the same results as with Fortran Exe.
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Expert Comment

by:ahoffmann
ID: 7119747
the fnction TRIDAG is called with an array for first 4 parameters, but the passed array is of size one elemnt.
That's ok (if the programmer wants this).
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by:ameba
ID: 7119843
Thanks, ahoffmann

>the passed array is of size one elemnt.

I don't think it's possible that 2 means 'upper bound' in Call Tridag(AA(2), ...)
Because there is a loop on that array (2 to NN) and passed NN is 51 or 501.

C-------------------------------------------------------------------
C     SOLVER FROM "NUMERICAL RECIPES", TRIDAG
C-------------------------------------------------------------------

     SUBROUTINE TRIDAG(AAA,AAB,AAC,ABB,E1,NN,BCT,BCB)

     INTEGER NN
     REAL*8 AAA(*),AAB(*),AAC(*),ABB(*),E1(20000)
     REAL*8 BET, GAM(20000)
     INTEGER BCT, BCB, N

     DO I=1,20000
          GAM(I)=1.0
          E1(I)=1.0
     ENDDO

     N = NN
     
     IF(BCB.GT.1) N=N-1
     IF(BCT.GT.1) N=N-1
     
     BET=AAB(1)
     E1(1)=ABB(1)/BET

     DO I=2,N
          GAM(I) = AAC(I-1) / BET
          BET = AAB(I) - AAA(I) * GAM(I)
          E1(I) = (ABB(I) - AAA(I) * E1(I-1)) / BET
     ENDDO
     
     DO I=N-1,1,-1
          E1(I)=E1(I)-GAM(I+1)*E1(I+1)
     ENDDO

     RETURN
     END


I think I got it right, although program results are a bit different.  For argument "AA(2)" I'm passing part of array, i.e. first element is AA(2).

But I don't know for sure that program is correct.  Maybe what you are saying is true and all other elements AAA(2)to AAA(50) are zero's...?
I don't have Fortran compiler here to check.
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by:ameba
ID: 7123361
Thanks.  Everything is working OK.  I have small difference when compared to Fortran results, but first 9 digits are the same. :-)

0.563085102878388 ' Fortran
0.563085102830859 ' VB
0.563085102830685 ' VB with option "Allow unrounded Floating Point Operations"
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Expert Comment

by:bruintje
ID: 7123645
ameba thanks, but that wasn't necessary i only posted it as *help* don't know if it would help you did most of it yourself
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