| Re: Solving elliptic equation in IDL [message #36250 is a reply to message #36102] |
Wed, 27 August 2003 15:17  |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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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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