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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} {} exponential_inv (@var{x}, @var{lambda}) |
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22 ## For each element of @var{x}, compute the quantile (the inverse of the |
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23 ## CDF) at @var{x} of the exponential distribution with parameter |
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24 ## @var{lambda}. |
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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: Quantile function of the exponential distribution |
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29 |
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30 function inv = exponential_inv (x, l) |
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31 |
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32 if (nargin != 2) |
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33 usage ("exponential_inv (x, lambda)"); |
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34 endif |
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35 |
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36 if (!isscalar (x) && !isscalar(l)) |
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37 [retval, x, l] = common_size (x, l); |
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38 if (retval > 0) |
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39 error ("exponential_inv: x and lambda 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 if (isscalar (x)) |
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44 sz = size (l); |
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45 else |
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46 sz = size (x); |
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47 endif |
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48 |
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49 inv = zeros (sz); |
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50 |
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51 k = find (!(l > 0) | (x < 0) | (x > 1) | isnan (x)); |
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52 if (any (k)) |
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53 inv(k) = NaN; |
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54 endif |
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55 |
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56 k = find ((x == 1) & (l > 0)); |
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57 if (any (k)) |
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58 inv(k) = Inf; |
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59 endif |
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60 |
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61 k = find ((x > 0) & (x < 1) & (l > 0)); |
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62 if (any (k)) |
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63 if isscalar (l) |
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64 inv(k) = - log (1 - x(k)) ./ l; |
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65 elseif isscalar (x) |
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66 inv(k) = - log (1 - x) ./ l(k); |
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67 else |
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68 inv(k) = - log (1 - x(k)) ./ l(k); |
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69 endif |
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70 endif |
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71 |
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72 endfunction |
