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<h3 class="section">7.7 Defining an FFTW module</h3>
<p>Rather than using the <code>include</code> statement to include the
<code>fftw3.f03</code> interface file in any subroutine where you want to
use FFTW, you might prefer to define an FFTW Fortran module. FFTW
does not install itself as a module, primarily because
<code>fftw3.f03</code> can be shared between different Fortran compilers while
modules (in general) cannot. However, it is trivial to define your
own FFTW module if you want. Just create a file containing:
<pre class="example"> module FFTW3
use, intrinsic :: iso_c_binding
include 'fftw3.f03'
end module
</pre>
<p>Compile this file into a module as usual for your compiler (e.g. with
<code>gfortran -c</code> you will get a file <code>fftw3.mod</code>). Now,
instead of <code>include 'fftw3.f03'</code>, whenever you want to use FFTW
routines you can just do:
<pre class="example"> use FFTW3
</pre>
<p>as usual for Fortran modules. (You still need to link to the FFTW
library, of course.)
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