Re: status lgamma V2.1.31 ?

[Paul Kienzle]

From: Rolf Fabian <address@hidden>
>Hi,
>
>can anybody with access to an Octave V2.1.31 installation

octave2.1:2> OCTAVE_VERSION 
OCTAVE_VERSION = 2.1.31

>give me some infos on status of built-in lgamma(x)
>by testing the following simple commands
>
>:1> lgamma(-1/2)

octave2.1:3> lgamma(-1/2)
ans = 1.2655

>
>My current installations V2.0.13 cygwin32
>(win95 precompiled) and V2.1.14 (OS/2) both fail 
>
>:1>lgamma(-1/2)  |-    1.2655     << FALSE
>
>because a non-zero imaginary part -+pi*i is expected,
>which seems to be rejected silently from the result.
>
>In case that an imag part is now correctly returned
>by V2.1.31, what's it's sign?
>Both -pi*i and +pi*i are actually possible, because
>the complex logarithm function is periodical with a
>period of 2*pi*i, so that the sign depends on some
>(more or less arbitrary) definition.
>
>Furthermore, what's the result for the poles on the
>negative real axis?
>:2> lgamma(-1)
>:3> lgamma(-2)

octave2.1:4> lgamma(-2)
 ***MESSAGE FROM ROUTINE DGAMMA IN LIBRARY SLATEC.
 ***FATAL ERROR, PROG ABORTED, TRACEBACK REQUESTED
 *  X IS A NEGATIVE INTEGER
 *  ERROR NUMBER = 4
 *   
 ***END OF MESSAGE
 
 ***JOB ABORT DUE TO FATAL ERROR.
0          ERROR MESSAGE SUMMARY
 LIBRARY    SUBROUTINE MESSAGE START             NERR     LEVEL     COUNT
 SLATEC     DGAMMA     X IS A NEGATIVE INTE         4         2         4

error: exception encountered in Fortran subroutine dlgams

>Is is always Inf or do any imag parts occur?
>
>Finally, does V2.1.31 allow for complex arguments now?
>:4> lgamma( 1+i)
>:5> lgamma(-1+i)

octave2.1:4> lgamma(1+i)
error: lgamma: unable to handle complex arguments

>
>Thanks for any feedback
>Rolf
>
>
>
>
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