Chris@19: Next: Reversing array dimensions, Chris@19: Previous: Calling FFTW from Modern Fortran, Chris@19: Up: Calling FFTW from Modern Fortran Chris@19:
FFTW provides a file fftw3.f03 that defines Fortran 2003
Chris@19: interfaces for all of its C routines, except for the MPI routines
Chris@19: described elsewhere, which can be found in the same directory as
Chris@19: fftw3.h (the C header file). In any Fortran subroutine where
Chris@19: you want to use FFTW functions, you should begin with:
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use, intrinsic :: iso_c_binding Chris@19: include 'fftw3.f03' Chris@19:Chris@19:
This includes the interface definitions and the standard
Chris@19: iso_c_binding module (which defines the equivalents of C
Chris@19: types). You can also put the FFTW functions into a module if you
Chris@19: prefer (see Defining an FFTW module).
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At this point, you can now call anything in the FFTW C interface Chris@19: directly, almost exactly as in C other than minor changes in syntax. Chris@19: For example: Chris@19: Chris@19:
type(C_PTR) :: plan Chris@19: complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out Chris@19: plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE) Chris@19: ... Chris@19: call fftw_execute_dft(plan, in, out) Chris@19: ... Chris@19: call fftw_destroy_plan(plan) Chris@19:Chris@19:
A few important things to keep in mind are: Chris@19: Chris@19:
type(C_PTR). Other C types are mapped in the
Chris@19: obvious way via the iso_c_binding standard: int turns
Chris@19: into integer(C_INT), fftw_complex turns into
Chris@19: complex(C_DOUBLE_COMPLEX), double turns into
Chris@19: real(C_DOUBLE), and so on. See FFTW Fortran type reference.
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Chris@19: fftw_execute
Chris@19: but rather using the more specialized functions like
Chris@19: fftw_execute_dft (see New-array Execute Functions).
Chris@19: However, you should execute the plan on the same arrays as the
Chris@19: ones for which you created the plan, unless you are especially
Chris@19: careful. See Plan execution in Fortran. To prevent
Chris@19: you from using fftw_execute by mistake, the fftw3.f03
Chris@19: file does not provide an fftw_execute interface declaration.
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Chris@19: 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.)
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