|
3133
|
1 ## Copyright (C) 1998 John W. Eaton |
|
|
2 ## |
|
|
3 ## This file is part of Octave. |
|
|
4 ## |
|
|
5 ## Octave is free software; you can redistribute it and/or modify it |
|
|
6 ## under the terms of the GNU General Public License as published by |
|
|
7 ## the Free Software Foundation; either version 2, or (at your option) |
|
|
8 ## any later version. |
|
|
9 ## |
|
|
10 ## Octave is distributed in the hope that it will be useful, but |
|
|
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
|
|
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
|
|
13 ## General Public License for more details. |
|
|
14 ## |
|
|
15 ## You should have received a copy of the GNU General Public License |
|
|
16 ## along with Octave; see the file COPYING. If not, write to the Free |
|
|
17 ## Software Foundation, 59 Temple Place - Suite 330, Boston, MA |
|
|
18 ## 02111-1307, USA. |
|
|
19 |
|
3321
|
20 ## -*- texinfo -*- |
|
|
21 ## @deftypefn {Mapping Function} {} gammai (@var{a}, @var{x}) |
|
|
22 ## Computes the incomplete gamma function, |
|
|
23 ## @iftex |
|
|
24 ## @tex |
|
|
25 ## $$ |
|
|
26 ## \gamma (a, x) = {\displaystyle\int_0^x e^{-t} t^{a-1} dt \over \Gamma (a)} |
|
|
27 ## $$ |
|
|
28 ## @end tex |
|
|
29 ## @end iftex |
|
|
30 ## @ifinfo |
|
3426
|
31 ## |
|
3321
|
32 ## @smallexample |
|
|
33 ## x |
|
|
34 ## 1 / |
|
|
35 ## gammai (a, x) = --------- | exp (-t) t^(a-1) dt |
|
|
36 ## gamma (a) / |
|
|
37 ## t=0 |
|
|
38 ## @end smallexample |
|
|
39 ## @end ifinfo |
|
3426
|
40 ## |
|
3321
|
41 ## If @var{a} is scalar, then @code{gammai (@var{a}, @var{x})} is returned |
|
|
42 ## for each element of @var{x} and vice versa. |
|
3426
|
43 ## |
|
3321
|
44 ## If neither @var{a} nor @var{x} is scalar, the sizes of @var{a} and |
|
|
45 ## @var{x} must agree, and @var{gammai} is applied element-by-element. |
|
|
46 ## @end deftypefn |
|
3408
|
47 ## @seealso{gamma and lgamma} |
|
3133
|
48 |
|
|
49 ## Author: jwe |
|
|
50 ## Created: 30 Jan 1998 |
|
|
51 |
|
|
52 function retval = gammai (a, x) |
|
|
53 |
|
|
54 if (nargin == 2) |
|
|
55 retval = gammainc (x, a); |
|
|
56 else |
|
|
57 usage ("gammai (a, x)"); |
|
|
58 endif |
|
|
59 |
|
|
60 endfunction |
