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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 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} {} finv (@var{x}, @var{m}, @var{n}) |
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21 ## For each component of @var{x}, compute the quantile (the inverse of |
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22 ## the CDF) at @var{x} of the F distribution with parameters @var{m} and |
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23 ## @var{n}. |
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24 ## @end deftypefn |
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25 |
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26 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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27 ## Description: Quantile function of the F distribution |
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28 |
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29 function inv = finv (x, m, n) |
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30 |
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31 if (nargin != 3) |
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32 print_usage (); |
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33 endif |
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34 |
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35 if (!isscalar (m) || !isscalar (n)) |
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36 [retval, x, m, n] = common_size (x, m, n); |
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37 if (retval > 0) |
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38 error ("finv: x, m and n must be of common size or scalar"); |
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39 endif |
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40 endif |
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41 |
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42 sz = size (x); |
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43 inv = zeros (sz); |
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44 |
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45 k = find ((x < 0) | (x > 1) | isnan (x) | !(m > 0) | !(n > 0)); |
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46 if (any (k)) |
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47 inv(k) = NaN; |
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48 endif |
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49 |
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50 k = find ((x == 1) & (m > 0) & (n > 0)); |
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51 if (any (k)) |
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52 inv(k) = Inf; |
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53 endif |
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54 |
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55 k = find ((x > 0) & (x < 1) & (m > 0) & (n > 0)); |
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56 if (any (k)) |
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57 if (isscalar (m) && isscalar (n)) |
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58 inv(k) = ((1 ./ betainv (1 - x(k), n / 2, m / 2) - 1) .* n ./ m); |
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59 else |
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60 inv(k) = ((1 ./ betainv (1 - x(k), n(k) / 2, m(k) / 2) - 1) |
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61 .* n(k) ./ m(k)); |
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62 endif |
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63 endif |
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64 |
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65 endfunction |
