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Fortran syntax help needed

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

ASKER CERTIFIED SOLUTION

Brian Mulder

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ameba

ASKER

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.

ameba

ASKER

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 :-)

ameba

ASKER

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.

ahoffmann

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).

ameba

ASKER

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.

ameba

ASKER

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"

Brian Mulder

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