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7.1 Overview of Fortran interface

FFTW provides a file fftw3.f03 that defines Fortran 2003 interfaces for all of its C routines, except for the MPI routines described elsewhere, which can be found in the same directory as fftw3.h (the C header file). In any Fortran subroutine where you want to use FFTW functions, you should begin with:

       use, intrinsic :: iso_c_binding
       include 'fftw3.f03'

This includes the interface definitions and the standard iso_c_binding module (which defines the equivalents of C types). You can also put the FFTW functions into a module if you prefer (see Defining an FFTW module).

At this point, you can now call anything in the FFTW C interface directly, almost exactly as in C other than minor changes in syntax. For example:

       type(C_PTR) :: plan
       complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out
       plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE)
       call fftw_execute_dft(plan, in, out)
       call fftw_destroy_plan(plan)

A few important things to keep in mind are: