| Re: Solving elliptic equation in IDL [message #36241 is a reply to message #36102] |
Thu, 28 August 2003 02:31   |
dallimor
Messages: 3
Registered: November 2002
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Junior Member |
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Mark, I just saw this thread and thought I'd make a comment. I did a
bit of interfacing between IDL and Fortran last year but I've just
moved and my code is in transit so I don't have any examples with me.
We did it a little differently but the principle was the same. The
comment I wanted to make was that this method removes any chance of
porting code because the "ATTRIBUTES VALUE" declaration is compiler
and OS specific. Also one other thing that we found was that to link
IDL to Compaq fortran the machine needed to have Visual C++ installed.
I never actually tracked down what libraries were required but I
couldn't get it to work without VC++ installed.
Did you build a dll or a dlm?
Chris Dallimore
Mark Hadfield <m.hadfield@niwa.co.nz> wrote in message news:<bijalf$5ba$1@newsreader.mailgate.org>...
> Mark Hadfield wrote:
>> Hi guys
>>
>> I want to solve an elliptic equation on a rectangular portion of the
>> (x,y) plane, specifically
>>
>> L(A) = f(x,y)
>>
>> where A is an unknown, scalar-valued 2D array, L is the Laplacian
>> operator (d2/dx2 + d2/dy2) and the RHS (forcing) term is a function of
>> space only. A is specified at the boundary.
>>
>> This can be done with an elliptic equation solver, of the type that
>> can be found in many general-purpose mathematical libraries. However a
>> Google search has not uncovered any IDL code to do this. So I have two
>> questions:
>>
>> - Does anyone have or know of an IDL elliptic equation solver?
>>
>> - If I choose to solve the equation in Fortran (Compaq Visual
>> Fortran 6.6B, IMSL Fortran Library,IDL 6.0, Windows 2000), what is the
>> path of least resistance for passing data between Fortran and IDL? A
>> DLM? Can I call a Fortran subroutine directly from IDL or will I
>> need to write glue code in C?
>
> Thanks for the replies. I thought I'd report progress to the group, in
> case it helps someone in future.
>
> I ended up using CALL_EXTERNAL to interface with the NCAR FISHPACK
> Fortran library. On the IDL side I wrote a wrapper routine to check
> arguments before passing them to CALL_EXTERNAL. On the Fortran side I
> wrote a glue routine to convert the "argc, argv" data passed by
> CALL_EXTERNAL to the format required by the FISHPACK routines. For the
> latter I found the following news threads useful:
>
> http://makeashorterlink.com/?G2E1525A5
> http://makeashorterlink.com/?C273235A5
>
> Below is an example of such a glue routine, written. It's similar to
> examples in the above threads, but illustrates one extra trick: using an
> "ATTRIBUTES VALUE" declaration on argc so this can be accessed in the
> Fortran code.
>
> --
> Mark Hadfield "Ka puwaha te tai nei, Hoea tatou"
> m.hadfield@niwa.co.nz
> National Institute for Water and Atmospheric Research (NIWA)
>
> --- testadd.f90 ---
>
> function testadd(argc, argv)
>
> !DEC$ ATTRIBUTES DLLEXPORT :: testadd
> !DEC$ ATTRIBUTES VALUE :: argc
>
> integer(kind=4) :: testadd
>
> integer(kind=4), intent(in) :: argc
> integer(kind=4), intent(in) :: argv(argc)
>
> if (argc.eq.4) then
> call add(%val(argv(1)),%val(argv(2)),%val(argv(3)),%val(argv(4)))
> testadd = 1
> else
> testadd = 0
> end if
>
> contains
>
> subroutine add(a, b, c, n)
>
> integer(kind=4), intent(in) :: n
> real(kind=4), intent(in) :: a(n), b(n)
> real(kind=4) :: c(n)
>
> c = a + b
>
> end subroutine add
>
> end function testadd
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