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Chris@42:FFTW provides a file fftw3.f03 that defines Fortran 2003
Chris@42: interfaces for all of its C routines, except for the MPI routines
Chris@42: described elsewhere, which can be found in the same directory as
Chris@42: fftw3.h (the C header file). In any Fortran subroutine where
Chris@42: you want to use FFTW functions, you should begin with:
Chris@42:
use, intrinsic :: iso_c_binding Chris@42: include 'fftw3.f03' Chris@42:
This includes the interface definitions and the standard
Chris@42: iso_c_binding module (which defines the equivalents of C
Chris@42: types). You can also put the FFTW functions into a module if you
Chris@42: prefer (see Defining an FFTW module).
Chris@42:
At this point, you can now call anything in the FFTW C interface Chris@42: directly, almost exactly as in C other than minor changes in syntax. Chris@42: For example: Chris@42:
Chris@42: Chris@42: Chris@42: Chris@42:type(C_PTR) :: plan Chris@42: complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out Chris@42: plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE) Chris@42: ... Chris@42: call fftw_execute_dft(plan, in, out) Chris@42: ... Chris@42: call fftw_destroy_plan(plan) Chris@42:
A few important things to keep in mind are: Chris@42:
Chris@42:type(C_PTR). Other C types are mapped in the
Chris@42: obvious way via the iso_c_binding standard: int turns
Chris@42: into integer(C_INT), fftw_complex turns into
Chris@42: complex(C_DOUBLE_COMPLEX), double turns into
Chris@42: real(C_DOUBLE), and so on. See FFTW Fortran type reference.
Chris@42:
Chris@42: fftw_execute
Chris@42: but rather using the more specialized functions like
Chris@42: fftw_execute_dft (see New-array Execute Functions).
Chris@42: However, you should execute the plan on the same arrays as the
Chris@42: ones for which you created the plan, unless you are especially
Chris@42: careful. See Plan execution in Fortran. To prevent
Chris@42: you from using fftw_execute by mistake, the fftw3.f03
Chris@42: file does not provide an fftw_execute interface declaration.
Chris@42:
Chris@42: ior (equivalent to ‘|’ in C). e.g. FFTW_MEASURE | FFTW_DESTROY_INPUT becomes ior(FFTW_MEASURE, FFTW_DESTROY_INPUT). (You can also use ‘+’ as long as you don’t try to include a given flag more than once.)
Chris@42:
Chris@42: | • Extended and quadruple precision in Fortran: | Chris@42: |
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Chris@42: