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/*!
* \file
* \brief Implementation of window functions
* \author Tony Ottosson, Tobias Ringstrom, Pal Frenger, Adam Piatyszek
* and Kumar Appaiah
*
* -------------------------------------------------------------------------
*
* Copyright (C) 1995-2010 (see AUTHORS file for a list of contributors)
*
* This file is part of IT++ - a C++ library of mathematical, signal
* processing, speech processing, and communications classes and functions.
*
* IT++ 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 of the License, or (at your option) any
* later version.
*
* IT++ 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 IT++. If not, see <http://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include <itpp/base/itcompat.h>
#include <itpp/signal/window.h>
#include <itpp/signal/poly.h>
#include <itpp/base/specmat.h>
#include <itpp/base/converters.h>
#include <itpp/base/math/trig_hyp.h>
#include <itpp/signal/transforms.h>
#include <itpp/base/operators.h>
namespace itpp
{
vec hamming(int n)
{
vec t(n);
if (n == 1)
t(0) = 0.08;
else
for (int i = 0;i < n;i++)
t[i] = (0.54 - 0.46 * std::cos(2.0 * pi * i / (n - 1)));
return t;
}
vec hanning(int n)
{
vec t(n);
for (int i = 0;i < n;i++)
t(i) = 0.5 * (1.0 - std::cos(2.0 * pi * (i + 1) / (n + 1)));
return t;
}
// matlab version
vec hann(int n)
{
vec t(n);
for (int i = 0;i < n;i++)
t(i) = 0.5 * (1.0 - std::cos(2.0 * pi * i / (n - 1)));
return t;
}
vec blackman(int n)
{
vec t(n);
for (int i = 0;i < n;i++)
t(i) = 0.42 - 0.5 * std::cos(2.0 * pi * i / (n - 1)) + 0.08 * std::cos(4.0 * pi * i / (n - 1));
return t;
}
vec triang(int n)
{
vec t(n);
if (n % 2) { // Odd
for (int i = 0; i < n / 2; i++)
t(i) = t(n - i - 1) = 2.0 * (i + 1) / (n + 1);
t(n / 2) = 1.0;
}
else
for (int i = 0; i < n / 2; i++)
t(i) = t(n - i - 1) = (2.0 * i + 1) / n;
return t;
}
vec sqrt_win(int n)
{
vec t(n);
if (n % 2) { // Odd
for (int i = 0; i < n / 2; i++)
t(i) = t(n - i - 1) = std::sqrt(2.0 * (i + 1) / (n + 1));
t(n / 2) = 1.0;
}
else
for (int i = 0; i < n / 2; i++)
t(i) = t(n - i - 1) = std::sqrt((2.0 * i + 1) / n);
return t;
}
vec chebwin(int n, double at)
{
it_assert((n > 0), "chebwin(): need a positive order n!");
if (n == 1) {
return vec("1");
}
at = at < 0 ? -at : at;
// compute the parameter beta
double beta = std::cosh(::acosh(pow10(at / 20)) / (n - 1));
vec k = (pi / n) * linspace(0, n - 1, n);
vec cos_k = cos(k);
// find the window's DFT coefficients
vec p = cheb(n - 1, beta * cos_k);
vec w(n); // the window vector
// Appropriate IDFT and filling up depending on even/odd n
if (is_even(n)) {
w = ifft_real(to_cvec(elem_mult(p, cos_k), elem_mult(p, -sin(k))));
int half_length = n / 2 + 1;
w = w.left(half_length) / w(1);
w = concat(reverse(w), w.right(n - half_length));
}
else {
w = ifft_real(to_cvec(p));
int half_length = (n + 1) / 2;
w = w.left(half_length) / w(0);
w = concat(reverse(w), w.right(n - half_length));
}
return w;
}
} // namespace itpp
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