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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} {} fpdf (@var{x}, @var{m}, @var{n}) |
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22 ## For each element of @var{x}, compute the probability density function |
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23 ## (PDF) at @var{x} of the F distribution with @var{m} and @var{n} |
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24 ## degrees of freedom. |
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25 ## @end deftypefn |
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26 |
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27 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> |
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28 ## Description: PDF of the F distribution |
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29 |
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30 function pdf = fpdf (x, m, n) |
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31 |
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32 if (nargin != 3) |
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33 usage ("fpdf (x, m, n)"); |
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34 endif |
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35 |
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36 if (!isscalar (m) || !isscalar (n)) |
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37 [retval, x, m, n] = common_size (x, m, n); |
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38 if (retval > 0) |
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39 error ("fpdf: x, m and n must be of common size or scalar"); |
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40 endif |
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41 endif |
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42 |
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43 sz = size (x); |
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44 pdf = zeros (sz); |
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45 |
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46 k = find (isnan (x) | !(m > 0) | !(n > 0)); |
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47 if (any (k)) |
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48 pdf(k) = NaN; |
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49 endif |
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50 |
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51 k = find ((x > 0) & (x < Inf) & (m > 0) & (n > 0)); |
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52 if (any (k)) |
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53 if (isscalar (m) && isscalar (n)) |
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54 tmp = m / n * x(k); |
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55 pdf(k) = (exp ((m / 2 - 1) .* log (tmp) |
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56 - ((m + n) / 2) .* log (1 + tmp)) |
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57 .* (m / n) ./ beta (m / 2, n / 2)); |
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58 else |
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59 tmp = m(k) .* x(k) ./ n(k); |
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60 pdf(k) = (exp ((m(k) / 2 - 1) .* log (tmp) |
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61 - ((m(k) + n(k)) / 2) .* log (1 + tmp)) |
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62 .* (m(k) ./ n(k)) ./ beta (m(k) / 2, n(k) / 2)); |
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63 endif |
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64 endif |
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65 |
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66 endfunction |
