[Octave-bug-tracker] [bug #60528] special function: betaincinv

[Paul Netsaver]

URL:
  <https://savannah.gnu.org/bugs/?60528>

                 Summary: special function: betaincinv
                 Project: GNU Octave
            Submitted by: netsaver
            Submitted on: Wed 05 May 2021 10:45:01 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error or Warning
                  Status: None
             Assigned to: None
         Originator Name: Netsaver Paul
        Originator Email: 
             Open/Closed: Open
                 Release: 6.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows

    _______________________________________________________

Details:

OCTAVE 6.2
betaincinv(1e-6,1,3)
% test printouts from the called 'betainc' follow:
x = 0.0000000, a = 1, b = 3
x = 1.0000000, a = 1, b = 3
x = 0.5000000, a = 1, b = 3
x = 0.2500000, a = 1, b = 3
x = 0.1250000, a = 1, b = 3
x = 0.0625000, a = 1, b = 3
x = 0.0312500, a = 1, b = 3
x = 0.0156250, a = 1, b = 3
x = 0.0078125, a = 1, b = 3
x = 0.0039062, a = 1, b = 3
x = 0.0019531, a = 1, b = 3
x = 0.0009766, a = 1, b = 3
x = 0.0009766, a = 1, b = 3
x = -0.0000006, a = 1, b = 3
error: betainc: X must be in the range [0, 1]
error: called from
    betainc at line 99 column 5
    betaincinv>@<anonymous> at line 172 column 25
    betaincinv>newton_method at line 236 column 15
    betaincinv at line 181 column 14

MATLAB 
betaincinv(1e-6,1,3)
ans = 3.333333e-07


out = betaincinv(p,m,n)
It is seen that the internal iterative procedure calls the direct beta
function with negative value of p and this cause the error.
It happens with p >= 1e-5 and m=1 and n>2 (not so uncommon values by the way,
e.g. p=1e-6, m=1, n=3 may happen in radar applications).
It seems that Matlab intercepts this case and get the results directly
dividing p by n: out = p/n.

Regards,
Paul Netsaver









    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?60528>

_______________________________________________
  Message sent via Savannah
  https://savannah.gnu.org/