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doc: Final grammarcheck and spellcheck before 3.6.0 release. * container.txi, aspell-octave.en.pws, expr.txi, vectorize.txi, accumarray.m, accumdim.m, interpft.m, strread.m, parseparams.m, warning_ids.m, cellfun.cc, help.cc: grammarcheck and spellcheck docstrings.
author Rik <octave@nomad.inbox5.com>
date Thu, 29 Dec 2011 06:05:00 -0800
parents 5f96b91b4e0c
children 72c96de7a403
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John W. Eaton <jwe@octave.org>
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1 ## Copyright (C) 2001-2011 Paul Kienzle
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {} interpft (@var{x}, @var{n})
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21 ## @deftypefnx {Function File} {} interpft (@var{x}, @var{n}, @var{dim})
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22 ##
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23 ## Fourier interpolation. If @var{x} is a vector, then @var{x} is
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24 ## resampled with @var{n} points. The data in @var{x} is assumed to be
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25 ## equispaced. If @var{x} is an array, then operate along each column of
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26 ## the array separately. If @var{dim} is specified, then interpolate
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27 ## along the dimension @var{dim}.
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28 ##
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29 ## @code{interpft} assumes that the interpolated function is periodic,
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30 ## and so assumptions are made about the endpoints of the interpolation.
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31 ##
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32 ## @seealso{interp1}
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33 ## @end deftypefn
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34
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35 ## Author: Paul Kienzle
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36 ## 2001-02-11
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37 ## * initial version
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38 ## 2002-03-17 aadler
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39 ## * added code to work on matrices as well
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40 ## 2006-05-25 dbateman
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41 ## * Make it matlab compatiable, cutting out the 2-D interpolation
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42
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43 function z = interpft (x, n, dim)
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44
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45 if (nargin < 2 || nargin > 3)
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46 print_usage ();
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47 endif
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48
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49 if (! (isscalar (n) && n == fix (n)))
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50 error ("interpft: N must be a scalar integer");
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51 endif
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52
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53 if (nargin == 2)
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54 if (isrow (x))
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55 dim = 2;
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56 else
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57 dim = 1;
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58 endif
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59 endif
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60
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61 nd = ndims (x);
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62
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63 if (dim < 1 || dim > nd)
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64 error ("interpft: invalid dimension DIM");
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65 endif
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66
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67 perm = [dim:nd, 1:(dim-1)];
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68 x = permute (x, perm);
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69 m = rows (x);
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70
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71 inc = max (1, fix (m/n));
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72 y = fft (x) / m;
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73 k = floor (m / 2);
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74 sz = size (x);
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75 sz(1) = n * inc - m;
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76
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77 idx = repmat ({':'}, nd, 1);
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78 idx{1} = 1:k;
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79 z = cat (1, y(idx{:}), zeros (sz));
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80 idx{1} = k+1:m;
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81 z = cat (1, z, y(idx{:}));
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82 z = n * ifft (z);
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83
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84 if (inc != 1)
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85 sz(1) = n;
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86 z = inc * reshape (z(1:inc:end), sz);
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87 endif
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88
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89 z = ipermute (z, perm);
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90
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91 endfunction
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92
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93
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94 %!demo
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95 %! t = 0 : 0.3 : pi; dt = t(2)-t(1);
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96 %! n = length (t); k = 100;
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97 %! ti = t(1) + [0 : k-1]*dt*n/k;
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98 %! y = sin (4*t + 0.3) .* cos (3*t - 0.1);
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99 %! yp = sin (4*ti + 0.3) .* cos (3*ti - 0.1);
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100 %! plot (ti, yp, 'g', ti, interp1(t, y, ti, 'spline'), 'b', ...
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101 %! ti, interpft (y, k), 'c', t, y, 'r+');
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102 %! legend ('sin(4t+0.3)cos(3t-0.1','spline','interpft','data');
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103
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104 %!shared n,y
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105 %! x = [0:10]'; y = sin(x); n = length (x);
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106 %!assert (interpft(y, n), y, 20*eps);
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107 %!assert (interpft(y', n), y', 20*eps);
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108 %!assert (interpft([y,y],n), [y,y], 20*eps);
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110 %% Test input validation
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111 %!error interpft ()
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112 %!error interpft (1)
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113 %!error interpft (1,2,3)
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114 %!error (interpft(1,[n,n]))
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115 %!error (interpft(1,2,0))
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116 %!error (interpft(1,2,3))