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1 ## Copyright (C) 1996, 1997 Kurt Hornik |
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2 ## |
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3 ## This program is free software; you can redistribute it and/or modify |
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4 ## it under the terms of the GNU General Public License as published by |
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5 ## the Free Software Foundation; either version 2, or (at your option) |
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6 ## any later version. |
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7 ## |
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8 ## This program is distributed in the hope that it will be useful, but |
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9 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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11 ## General Public License for more details. |
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12 ## |
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13 ## You should have received a copy of the GNU General Public License |
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14 ## along with this file. If not, write to the Free Software Foundation, |
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15 ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
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16 |
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17 ## -*- texinfo -*- |
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18 ## @deftypefn {Function File} {} discrete_inv (@var{x}, @var{v}, @var{p}) |
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19 ## For each component of @var{x}, compute the quantile (the inverse of |
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20 ## the CDF) at @var{x} of the univariate distribution which assumes the |
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21 ## values in @var{v} with probabilities @var{p}. |
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22 ## @end deftypefn |
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23 |
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24 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> |
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25 ## Description: Quantile function of a discrete distribution |
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26 |
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27 function inv = discrete_inv (x, v, p) |
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28 |
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29 if (nargin != 3) |
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30 usage ("discrete_inv (x, v, p)"); |
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31 endif |
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32 |
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33 [r, c] = size (x); |
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34 |
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35 if (! is_vector (v)) |
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36 error ("discrete_inv: v must be a vector"); |
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37 elseif (! is_vector (p) || (length (p) != length (v))) |
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38 error ("discrete_inv: p must be a vector with length (v) elements"); |
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39 elseif (! (all (p >= 0) && any (p))) |
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40 error ("discrete_inv: p must be a nonzero, nonnegative vector"); |
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41 endif |
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42 |
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43 n = r * c; |
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44 x = reshape (x, 1, n); |
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45 m = length (v); |
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46 [v, ind] = sort (v); |
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47 s = reshape (cumsum (p / sum (p)), m, 1); |
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48 |
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49 inv = NaN * ones (n, 1); |
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50 if (any (k = find (x == 0))) |
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51 inv(k) = -Inf * ones (1, length (k)); |
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52 endif |
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53 if (any (k = find (x == 1))) |
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54 inv(k) = v(m) * ones (1, length (k)); |
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55 endif |
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56 if (any (k = find ((x > 0) & (x < 1)))) |
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57 n = length (k); |
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58 ## --FIXME-- |
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59 ## This does not work! |
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60 inv(k) = v(sum ((ones (m, 1) * x(k)) > (s * ones (1, n))) + 1); |
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61 endif |
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62 |
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63 inv = reshape (inv, r, c); |
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64 |
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65 endfunction |
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66 |
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67 |
