#12521: evaluate log gamma for complex input
------------------------------------+---------------------------------------
Reporter: kcrisman | Owner: AlexGhitza
Type: defect | Status: new
Priority: critical | Milestone: sage-5.11
Component: basic arithmetic | Resolution:
Keywords: lgamma log_gamma | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
------------------------------------+---------------------------------------
Comment (by eviatarbach):
Paul, could you please comment on this code for
`sage/rings/real_mpfr.pyx`?
{{{
def log_gamma(self):
cdef RealNumber x = self._new()
cdef int sign
parent = (<RealField_class>self._parent)
if parent.__prec > SIG_PREC_THRESHOLD: sig_on()
mpfr_lgamma(x.value, &sign, self.value, parent.rnd)
if parent.__prec > SIG_PREC_THRESHOLD: sig_off()
if not mpfr_sgn(self.value) < 0:
return x
cdef RealNumber v = self._new()
mpfr_div_si((<RealNumber>v).value, self.value, 2, parent.rnd)
return parent.complex_field()(x, parent.pi() *
(2 * (v - 1).ceil() + 1))
}}}
This correctly computes the principal branch. However, I'm concerned about
precision; the result of `lgamma` is presumably guaranteed to be correct
up to the precision of the input, but after doing some arithmetic it might
not be. Is there any way to fix this?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12521#comment:10>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
