fft_utils.cc
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	/**
	* file fft_utils.cc
	*
	* @author Till Junge <till.junge@altermail.ch>
	*
	* @date 11 Dec 2017
	*
	* @brief implementation of fft utilities
	*
	* @section LICENCE
	*
	* Copyright (C) 2017 Till Junge
	*
	* µSpectre is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation, either version 3, or (at
	* your option) any later version.
	*
	* µSpectre is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with GNU Emacs; see the file COPYING. If not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* Boston, MA 02111-1307, USA.
	*/

	#include "fft/fft_utils.hh"


	namespace muSpectre {

	/* ---------------------------------------------------------------------- */
	std::valarray<Real> fft_freqs(size_t nb_samples) {
	std::valarray<Real> retval(nb_samples);
	Int N = (nb_samples-1)/2 + 1; // needs to be signed int for neg freqs
	for (Int i = 0; i < N; ++i) {
	retval[i] = i;
	}
	for (Int i = N; i < Int(nb_samples); ++i) {
	retval[i] = -Int(nb_samples)/2+i-N;
	}
	return retval;
	}

	/* ---------------------------------------------------------------------- */
	std::valarray<Real> fft_freqs(size_t nb_samples, Real length) {
	return fft_freqs(nb_samples)/length;
	}


	} // muSpectre