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\section{Applications} |
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\label{sec:apps} |
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\subsection{Example: wrapping C library \texttt{fftw}} |
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\label{sec:wrapfftw} |
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Here follows a simple example how to use \fpy to generate a wrapper |
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for C functions. Let us create a FFT code using the functions in FFTW |
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library. I'll assume that the library \texttt{fftw} is configured with |
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\texttt{-{}-enable-shared} option. |
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Here is the wrapper for the typical usage of FFTW: |
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\begin{verbatim} |
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/* File: wrap_dfftw.c */ |
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#include <dfftw.h> |
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extern void dfftw_one(fftw_complex *in,fftw_complex *out,int *n) { |
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fftw_plan p; |
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p = fftw_create_plan(*n,FFTW_FORWARD,FFTW_ESTIMATE); |
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fftw_one(p,in,out); |
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fftw_destroy_plan(p); |
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} |
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\end{verbatim} |
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and here follows the corresponding siganture file (created manually): |
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\begin{verbatim} |
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!%f90 |
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! File: fftw.f90 |
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module fftw |
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interface |
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subroutine dfftw_one(in,out,n) |
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integer n |
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complex*16 in(n),out(n) |
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intent(out) out |
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intent(hide) n |
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end subroutine dfftw_one |
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end interface |
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end module fftw |
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\end{verbatim} |
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Now let us generate the Python C/API module with \fpy: |
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\begin{verbatim} |
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f2py fftw.f90 |
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\end{verbatim} |
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and compile it |
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\begin{verbatim} |
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gcc -shared -I/numeric/include -I`f2py -I` -L/numeric/lib -ldfftw \ |
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-o fftwmodule.so -DNO_APPEND_FORTRAN fftwmodule.c wrap_dfftw.c |
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\end{verbatim} |
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In Python: |
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\begin{verbatim} |
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>>> from Numeric import * |
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>>> from fftw import * |
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>>> print dfftw_one.__doc__ |
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Function signature: |
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out = dfftw_one(in) |
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Required arguments: |
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in : input rank-1 array('D') with bounds (n) |
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Return objects: |
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out : rank-1 array('D') with bounds (n) |
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>>> print dfftw_one([1,2,3,4]) |
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[ 10.+0.j -2.+2.j -2.+0.j -2.-2.j] |
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>>> |
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\end{verbatim} |
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