From help-octave-request at bevo dot che dot wisc dot edu  Mon Sep  4 02:51:56 2000
Subject: status lgamma V2.1.31 ?
From: Rolf Fabian <fabian at tu-cottbus dot de>
To: "'help-octave UWISC'" <help-octave at bevo dot che dot wisc dot edu>
Date: Mon, 4 Sep 2000 09:49:44 +0200

Hi,

can anybody with access to an Octave V2.1.31 installation
give me some infos on status of built-in lgamma(x)
by testing the following simple commands

:1> lgamma(-1/2)

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)
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)

Thanks for any feedback
Rolf




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