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1 ## Copyright (C) 1995, 1996, 1997 Kurt Hornik |
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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 2, or (at your option) |
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8 ## 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, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} moment (@var{x}, @var{p}, @var{opt}, @var{dim}) |
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22 ## If @var{x} is a vector, compute the @var{p}-th moment of @var{x}. |
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23 ## |
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24 ## If @var{x} is a matrix, return the row vector containing the |
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25 ## @var{p}-th moment of each column. |
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26 ## |
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27 ## With the optional string opt, the kind of moment to be computed can |
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28 ## be specified. If opt contains @code{"c"} or @code{"a"}, central |
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29 ## and/or absolute moments are returned. For example, |
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30 ## |
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31 ## @example |
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32 ## moment (x, 3, "ac") |
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33 ## @end example |
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34 ## |
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35 ## @noindent |
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36 ## computes the third central absolute moment of @var{x}. |
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37 ## |
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38 ## If the optional argument @var{dim} is supplied, work along dimension |
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39 ## @var{dim}. |
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40 ## @end deftypefn |
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41 |
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42 ## Can easily be made to work for continuous distributions (using quad) |
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43 ## as well, but how does the general case work? |
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44 |
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45 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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46 ## Description: Compute moments |
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47 |
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48 function m = moment (x, p, opt1, opt2) |
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49 |
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50 if ((nargin < 2) || (nargin > 4)) |
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51 print_usage (); |
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52 endif |
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53 |
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54 need_dim = 0; |
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55 |
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56 if (nargin == 2) |
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57 opt = ""; |
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58 need_dim = 1; |
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59 elseif (nargin == 3) |
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60 if (ischar (opt1)) |
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61 opt = opt1; |
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62 need_dim = 1; |
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63 else |
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64 dim = opt1; |
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65 opt = ""; |
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66 endif |
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67 elseif (nargin == 4) |
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68 if (ischar (opt1)) |
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69 opt = opt1; |
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70 dim = opt2; |
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71 elseif (ischar (opt2)) |
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72 opt = opt2; |
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73 dim = opt1; |
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74 else |
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75 error ("moment: expecting opt to be a string"); |
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76 endif |
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77 else |
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78 print_usage (); |
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79 endif |
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80 |
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81 if (need_dim) |
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82 t = find (size (x) != 1); |
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83 if (isempty (t)) |
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84 dim = 1; |
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85 else |
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86 dim = t(1); |
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87 endif |
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88 endif |
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89 |
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90 sz = size (x); |
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91 n = sz (dim); |
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92 |
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93 if (numel (x) < 1) |
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94 error ("moment: x must not be empty"); |
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95 endif |
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96 |
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97 if any (opt == "c") |
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98 rng = ones (1, length (sz)); |
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99 rng(dim) = sz(dim); |
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100 x = x - repmat (sum (x, dim), rng) / n; |
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101 endif |
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102 if any (opt == "a") |
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103 x = abs (x); |
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104 endif |
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105 |
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106 m = sum (x .^ p, dim) / n; |
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107 |
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108 endfunction |
