#10849: behaviour of gamma strangely sensitive
-------------------------+--------------------------------------------------
Reporter: dsm | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone:
Component: symbolics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-------------------------+--------------------------------------------------
Whether you get the correct result or a spurious ValueError in evaluating
some gamma expressions depends upon things it shouldn't.
This comes from [http://groups.google.com/group/sage-
support/browse_thread/thread/3b7126c1a29db091# a sage-support thread]; I
looked and couldn't find it here, but possibly it's a duplicate. (I have
bad luck with trac.)
See also [http://demo.sagenb.org/home/pub/66/ this worksheet].
Here's a relatively simple test case, in 4.6.1 and 4.6.2.rc0:
{{{
sage: x = var("x")
sage: f = exp(gamma(I*x-1/2).subs(x=I*x))
sage: g=f.operands()[0]
sage: g, type(g)
(gamma(-x - 1/2), <type 'sage.symbolic.expression.Expression'>)
sage: g(x=0)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
/Applications/sage_devel/<ipython console> in <module>()
/Applications/sage/local/lib/python2.6/site-
packages/sage/symbolic/expression.so in
sage.symbolic.expression.Expression.__call__
(sage/symbolic/expression.cpp:15657)()
/Applications/sage/local/lib/python2.6/site-packages/sage/symbolic/ring.so
in sage.symbolic.ring.SymbolicRing._call_element_
(sage/symbolic/ring.cpp:6537)()
/Applications/sage/local/lib/python2.6/site-
packages/sage/symbolic/expression.so in
sage.symbolic.expression.Expression.substitute
(sage/symbolic/expression.cpp:15036)()
/Applications/sage/local/lib/python2.6/site-
packages/sage/symbolic/pynac.so in sage.symbolic.pynac.py_doublefactorial
(sage/symbolic/pynac.cpp:9463)()
ValueError: argument must be >= -1
sage: g(x=0)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
[ ... duplicate removed; this is merely to show it's not only the first
call which has problems ]
ValueError: argument must be >= -1
sage: gamma(-x-1/2)*g
gamma(-x - 1/2)^2
sage: g(x=0)
-2*sqrt(pi)
}}}
That is, merely performing the should-be-irrelevant "gamma(-x-1/2)*g" op
makes g(x=0) start working. Instrumenting it shows that that
py_doublefactorial gets a -3 the first time instead of the 1 it does the
second time, but I couldn't quite follow the calling order to isolate the
error.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10849>
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 post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en.
