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annotate scripts/general/interpft.m @ 20830:b65888ec820e draft default tip gccjit
dmalcom gcc jit import
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date | Fri, 27 Feb 2015 16:59:36 +0100 |
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1 ## Copyright (C) 2001-2015 Paul Kienzle |
5837 | 2 ## |
3 ## This file is part of Octave. | |
4 ## | |
5 ## Octave is free software; you can redistribute it and/or modify it | |
6 ## under the terms of the GNU General Public License as published by | |
7016 | 7 ## the Free Software Foundation; either version 3 of the License, or (at |
8 ## your option) any later version. | |
5837 | 9 ## |
10 ## Octave is distributed in the hope that it will be useful, but | |
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 ## General Public License for more details. | |
14 ## | |
15 ## You should have received a copy of the GNU General Public License | |
7016 | 16 ## along with Octave; see the file COPYING. If not, see |
17 ## <http://www.gnu.org/licenses/>. | |
5837 | 18 |
19 ## -*- texinfo -*- | |
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20 ## @deftypefn {Function File} {} interpft (@var{x}, @var{n}) |
5837 | 21 ## @deftypefnx {Function File} {} interpft (@var{x}, @var{n}, @var{dim}) |
22 ## | |
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23 ## Fourier interpolation. |
5837 | 24 ## |
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25 ## If @var{x} is a vector then @var{x} is resampled with @var{n} points. The |
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26 ## data in @var{x} is assumed to be equispaced. If @var{x} is a matrix or an |
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27 ## N-dimensional array, the interpolation is performed on each column of |
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28 ## @var{x}. |
5837 | 29 ## |
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30 ## If @var{dim} is specified, then interpolate along the dimension @var{dim}. |
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31 ## |
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32 ## @code{interpft} assumes that the interpolated function is periodic, and so |
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33 ## assumptions are made about the endpoints of the interpolation. |
5837 | 34 ## @seealso{interp1} |
35 ## @end deftypefn | |
36 | |
37 ## Author: Paul Kienzle | |
38 ## 2001-02-11 | |
39 ## * initial version | |
40 ## 2002-03-17 aadler | |
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41 ## * added code to work on matrices as well |
5837 | 42 ## 2006-05-25 dbateman |
43 ## * Make it matlab compatiable, cutting out the 2-D interpolation | |
44 | |
45 function z = interpft (x, n, dim) | |
46 | |
47 if (nargin < 2 || nargin > 3) | |
48 print_usage (); | |
49 endif | |
50 | |
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51 if (! (isscalar (n) && n == fix (n))) |
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52 error ("interpft: N must be a scalar integer"); |
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53 endif |
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54 |
5837 | 55 if (nargin == 2) |
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56 if (isrow (x)) |
5837 | 57 dim = 2; |
58 else | |
59 dim = 1; | |
60 endif | |
61 endif | |
62 | |
5838 | 63 nd = ndims (x); |
5837 | 64 |
65 if (dim < 1 || dim > nd) | |
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66 error ("interpft: invalid dimension DIM"); |
5837 | 67 endif |
68 | |
5838 | 69 perm = [dim:nd, 1:(dim-1)]; |
70 x = permute (x, perm); | |
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71 m = rows (x); |
5837 | 72 |
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73 inc = ceil (m/n); |
5837 | 74 y = fft (x) / m; |
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75 k = ceil (m / 2); |
5838 | 76 sz = size (x); |
5837 | 77 sz(1) = n * inc - m; |
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78 |
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79 idx = repmat ({':'}, nd, 1); |
5837 | 80 idx{1} = 1:k; |
5838 | 81 z = cat (1, y(idx{:}), zeros (sz)); |
5837 | 82 idx{1} = k+1:m; |
83 z = cat (1, z, y(idx{:})); | |
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84 |
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85 ## When m is an even number of rows, the FFT has a single Nyquist bin. |
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86 ## If zero-padded above, distribute the value of the Nyquist bin evenly |
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87 ## between the new corresponding positive and negative frequency bins. |
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88 if (sz(1) > 0 && k == m/2) |
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89 idx{1} = n * inc - k + 1; |
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90 tmp = z(idx{:}) / 2; |
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91 z(idx{:}) = tmp; |
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92 idx{1} = k + 1; |
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93 z(idx{:}) = tmp; |
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94 endif |
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95 |
5837 | 96 z = n * ifft (z); |
97 | |
98 if (inc != 1) | |
99 sz(1) = n; | |
5838 | 100 z = inc * reshape (z(1:inc:end), sz); |
5837 | 101 endif |
102 | |
103 z = ipermute (z, perm); | |
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104 |
5837 | 105 endfunction |
106 | |
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107 |
5837 | 108 %!demo |
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109 %! clf; |
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110 %! t = 0 : 0.3 : pi; dt = t(2)-t(1); |
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111 %! n = length (t); k = 100; |
5837 | 112 %! ti = t(1) + [0 : k-1]*dt*n/k; |
113 %! y = sin (4*t + 0.3) .* cos (3*t - 0.1); | |
114 %! yp = sin (4*ti + 0.3) .* cos (3*ti - 0.1); | |
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115 %! plot (ti, yp, 'g', ti, interp1(t, y, ti, "spline"), 'b', ... |
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116 %! ti, interpft (y, k), 'c', t, y, "r+"); |
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117 %! legend ("sin(4t+0.3)cos(3t-0.1)", "spline", "interpft", "data"); |
5837 | 118 |
119 %!shared n,y | |
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120 %! x = [0:10]'; y = sin(x); n = length (x); |
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121 %!assert (interpft (y, n), y, 20*eps); |
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122 %!assert (interpft (y', n), y', 20*eps); |
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123 %!assert (interpft ([y,y],n), [y,y], 20*eps); |
5837 | 124 |
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125 ## Test case with complex input from bug #39566 |
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126 %!test |
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127 %! x = (1 + j) * [1:4]'; |
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128 %! y = ifft ([15 + 15*j; -6; -1.5 - 1.5*j; 0; -1.5 - 1.5*j; -6*j]); |
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129 %! assert (interpft (x, 6), y, 10*eps); |
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130 |
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131 ## Test for correct spectral symmetry with even/odd lengths |
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132 %!assert (max (abs (imag (interpft ([1:8], 20)))), 0, 20*eps); |
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133 %!assert (max (abs (imag (interpft ([1:8], 21)))), 0, 21*eps); |
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134 %!assert (max (abs (imag (interpft ([1:9], 20)))), 0, 20*eps); |
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135 %!assert (max (abs (imag (interpft ([1:9], 21)))), 0, 21*eps); |
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136 |
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137 ## Test input validation |
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138 %!error interpft () |
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139 %!error interpft (1) |
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140 %!error interpft (1,2,3) |
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141 %!error <N must be a scalar integer> interpft (1,[2,2]) |
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142 %!error <N must be a scalar integer> interpft (1,2.1) |
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143 %!error <invalid dimension DIM> interpft (1,2,0) |
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144 %!error <invalid dimension DIM> interpft (1,2,3) |
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145 |