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1 ## Copyright (C) 2000 Kai Habel |
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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} {@var{z} =} trapz (@var{y}) |
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21 ## @deftypefnx {Function File} {@var{z} =} trapz (@var{x}, @var{y}) |
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22 ## @deftypefnx {Function File} {@var{z} =} trapz (@dots{}, @var{dim}) |
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23 ## |
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24 ## Numerical integration using trapezoidal method. @code{trapz |
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25 ## (@var{y})} computes the integral of the @var{y} along the first |
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26 ## non singleton dimension. If the argument @var{x} is omitted a |
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27 ## equally spaced vector is assumed. @code{trapz (@var{x}, @var{y})} |
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28 ## evaluates the integral with respect to @var{x}. |
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29 ## |
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30 ## @seealso{cumtrapz} |
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31 ## @end deftypefn |
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32 |
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33 ## Author: Kai Habel <kai.habel@gmx.de> |
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34 ## |
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35 ## also: June 2000 - Paul Kienzle (fixes,suggestions) |
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36 ## 2006-05-12 David Bateman - Modified for NDArrays |
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37 |
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38 function z = trapz (x, y, dim) |
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39 |
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40 |
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41 if (nargin < 1) || (nargin > 3) |
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42 print_usage (); |
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43 endif |
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44 |
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45 nd = ndims (x); |
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46 sz = size (x); |
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47 |
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48 have_x = false; |
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49 have_dim = false; |
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50 if (nargin == 3) |
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51 have_x = true; |
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52 have_dim = true; |
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53 endif |
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54 if (nargin == 2) |
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55 if (! size_equal (x, y) && isscalar (y)) |
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56 dim = y; |
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57 have_dim = true; |
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58 else |
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59 have_x = true; |
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60 endif |
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61 endif |
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62 |
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63 if (! have_dim) |
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64 ## Find the first singleton dimension. |
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65 dim = 0; |
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66 while (dim < nd && sz(dim+1) == 1) |
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67 dim++; |
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68 endwhile |
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69 dim++; |
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70 if (dim > nd) |
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71 dim = 1; |
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72 endif |
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73 else |
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74 dim = floor (dim); |
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75 if (dim < 1 || dim > nd) |
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76 error ("cumtrapz: invalid dimension along which to sort"); |
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77 endif |
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78 endif |
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79 |
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80 n = sz(dim); |
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81 idx1 = cell (); |
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82 for i = 1:nd |
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83 idx1{i} = 1:sz(i); |
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84 endfor |
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85 idx2 = idx1; |
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86 idx1{dim} = 2 : n; |
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87 idx2{dim} = 1 : (n - 1); |
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88 |
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89 if (! have_x) |
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90 z = 0.5 * sum (x(idx1{:}) + x(idx2{:}), dim); |
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91 else |
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92 if (! size_equal (x, y)) |
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93 error ("cumtrapz: x and y must have same shape"); |
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94 endif |
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95 z = 0.5 * sum ((x(idx1{:}) - x(idx2{:})) .* |
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96 (y(idx1{:}) + y(idx2{:})), dim); |
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97 endif |
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98 endfunction |
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99 |
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100 %!assert (trapz(1:5), 12) |
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101 %!assert (trapz(0:0.5:2,1:5), 6) |
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102 %!assert (trapz([1:5;1:5],2),[12;12]) |
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103 %!assert (trapz([1:5;1:5].',1),[12,12]) |
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104 %!assert (trapz([0:0.5:2;0:0.5:2],[1:5;1:5],2),[6;6]) |
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105 %!assert (trapz([0:0.5:2;0:0.5:2].',[1:5;1:5].',1),[6,6]) |
