Mercurial > jwe > octave
view scripts/signal/blackman.m @ 31170:06c76eca5f95 default tip @
maint: merge stable to default
author | John W. Eaton <jwe@octave.org> |
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date | Fri, 29 Jul 2022 12:02:42 -0400 |
parents | 5d3faba0342e |
children |
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######################################################################## ## ## Copyright (C) 1995-2022 The Octave Project Developers ## ## See the file COPYRIGHT.md in the top-level directory of this ## distribution or <https://octave.org/copyright/>. ## ## This file is part of Octave. ## ## Octave 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. ## ## Octave 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 Octave; see the file COPYING. If not, see ## <https://www.gnu.org/licenses/>. ## ######################################################################## ## -*- texinfo -*- ## @deftypefn {} {@var{c} =} blackman (@var{m}) ## @deftypefnx {} {@var{c} =} blackman (@var{m}, "periodic") ## @deftypefnx {} {@var{c} =} blackman (@var{m}, "symmetric") ## Return the filter coefficients of a @nospell{Blackman} window of length ## @var{m}. ## ## If the optional argument @qcode{"periodic"} is given, the periodic form ## of the window is returned. This is equivalent to the window of length ## @var{m}+1 with the last coefficient removed. The optional argument ## @qcode{"symmetric"} is equivalent to not specifying a second argument. ## ## For a definition of the @nospell{Blackman} window, see, e.g., ## @nospell{A.V. Oppenheim & R. W. Schafer}, ## @cite{Discrete-Time Signal Processing}. ## @end deftypefn function c = blackman (m, opt) if (nargin < 1) print_usage (); endif if (! (isscalar (m) && m > 0 && m == fix (m))) error ("blackman: M must be a positive integer"); endif N = m - 1; if (nargin == 2) switch (opt) case "periodic" N = m; case "symmetric" ## Default option, same as no option specified. otherwise error ('blackman: window type must be either "periodic" or "symmetric"'); endswitch endif if (m == 1) c = 1; else m -= 1; k = (0 : m)' / N; c = 0.42 - 0.5 * cos (2 * pi * k) + 0.08 * cos (4 * pi * k); endif endfunction %!assert (blackman (1), 1) %!assert (blackman (2), zeros (2,1), 1e-6) %!assert (blackman (15), flip (blackman (15)), 5*eps) %!assert (blackman (16), flip (blackman (16)), 5*eps) %!test %! N = 9; %! A = blackman (N); %! assert (A(ceil (N/2)), 1, 1e-6); %! assert ([A(1), A(length (A))], zeros (1,2), 1e-6); %!assert (blackman (15), blackman (15, "symmetric")) %!assert (blackman (16)(1:15), blackman (15, "periodic")) %!test %! N = 16; %! A = blackman (N, "periodic"); %! assert (A(N/2 + 1), 1, 1e-6); %!error <Invalid call> blackman () %!error blackman (0.5) %!error blackman (-1) %!error blackman (ones (1,4)) %!error blackman (1, "invalid")