#12521: evaluate log gamma for complex input
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Reporter: kcrisman | Owner: AlexGhitza
Type: defect | Status: new
Priority: major | Milestone: sage-5.1
Component: basic arithmetic | Resolution:
Keywords: lgamma log_gamma | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by zimmerma):
by the way, MPFR provides two functions: {{{mpfr_lngamma}}} indeed returns
{{{NaN}}} between
{{{-2k-1}}} and {{{-2k}}} for {{{k}}} a non-negative integer.
However there is another function {{{mpfr_lgamma}}} which returns
{{{log(abs(gamma(x)))}}},
and separately the sign of {{{gamma(x)}}}. It suffices to add {{{pi*I}}}
when the sign is
negative.
This would solve the problem at least for real input.
Paul
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12521#comment:4>
Sage <http://www.sagemath.org>
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