R devel - Jul 2007 - Accuracy of qt for df=1 (PR#9804)

Full_Name: Morten Welinder
Version: 2.2.0
OS: Linux
Submission from: (NULL) (216.223.241.229)


The qt function for df=1 is implemented as...

    q = - tan((P+1) * M_PI_2);

Adding 1 kills accuracy for P near 0.  A better way is to use

   q = cot(P * M_PI_2);
or
   q = 1/tan(P * M_PI_2);

>>>>> "MW" == Morten Welinder <mwelinder at
gmail.com>
>>>>>     on Tue, 24 Jul 2007 17:18:09 +0200 (CEST) writes:
    MW> Full_Name: Morten Welinder
    MW> Version: 2.2.0
    MW> OS: Linux
    MW> Submission from: (NULL) (216.223.241.229)


    MW> The qt function for df=1 is implemented as...

    MW> q = - tan((P+1) * M_PI_2);

    MW> Adding 1 kills accuracy for P near 0.  A better way is to use

    MW> q = cot(P * M_PI_2);
    MW> or
    MW> q = 1/tan(P * M_PI_2);


Yes, indeed, thanks a lot, Morten!!

     ((BTW: you should really upgrade your version of R))

Best regards,
Martin