Re: octave-1.0.11 Comments and Queries

[Jim Van Zandt]

John -

Thanks!  This must be why my calculations of the chi-square function
have been wrong with recent releases of Octave.  (I have downgraded to
2.0.5, until Dirk Eddelbuettel <address@hidden>, the Debian
maintainer, can incorporate your patch.)

                         - Jim Van Zandt

> | B: It seems gammai(a,x) is the wrong way round, in that it gives the
> | result you would expect if x were the exponent and a were the
> | integration limit. It turns out, looking at the m-file which calls
> | gammainc as gammainc(x,a), and testing gammainc, that it is gammainc
> | which is the wrong way round (i.e. gammainc(x,a) gives the result
> | you would expect if x were the exponent and a the limit).
> | 
> | Is this a bug or is it intentional? (I've changed the gammai m-file
> | which is easy, but it might be worth re-compiling the gammainc .oct
> | file since that's where the trouble really is).
> 
> This is a bug.  Here's my fix:
> 
> *** liboctave/lo-specfun.cc~  Thu Feb 19 01:28:15 1998
> --- liboctave/lo-specfun.cc   Mon Apr  6 00:27:28 1998
> ***************
> *** 477,483 ****
>   gammainc (double x, double a)
>   {
>     double retval;
> !   F77_XFCN (xdgami, XDGAMI, (x, a, retval));
>     return retval;
>   }
>   
> --- 477,483 ----
>   gammainc (double x, double a)
>   {
>     double retval;
> !   F77_XFCN (xdgami, XDGAMI, (a, x, retval));
>     return retval;
>   }
>   
> *** libcruft/slatec-fn/xdgami.f~      Sun Nov 30 18:22:24 1997
> --- libcruft/slatec-fn/xdgami.f       Mon Apr  6 00:26:16 1998
> ***************
> *** 1,5 ****
> !       subroutine xdgami (x, a, result)
> !       double precision x, a, result, dgami
> !       result = dgami (x, a)
>         return
>         end
> --- 1,5 ----
> !       subroutine xdgami (a, x, result)
> !       double precision a, x, result, dgami
> !       result = dgami (a, x)
>         return
>         end
> 
> However, the order of the arguments in the gammai and gammainc
> functions is correct.  gammainc is compatible with Matlab, gammai is
> compatible with older versions of Octave.