[GiNaC-devel] Bugfix "commit 97ef604e breaks evaluation of some G-polylogs"

[Stefan Weinzierl]

Hello,

the attached patch corrects and supersedes the patches
97ef604e "G_numeric: fix numeric evaluation with trailing zeros and y != 
1."
and
9e80b0d3 "G_numeric: fix evaluation with y == 1".

The original motivation for patch 97ef604e was to make sure that Hoelder 
convolution
is only used if there no trailing zeros.
Patch 97ef604e delegated the case of trailing zeros to G_do_trafo, which 
correctly
removes the trailing zeros, but in addition also performed the 
transformation described
in sect. 5.3 of hep-ph/0410259 ("convergence transformation").
The inappropriate call of the convergence transformation is the cause of 
the new bug reported at
http://www.cebix.net/pipermail/ginac-list/2014-September/002011.html

The patch 9e80b0d3 cures the symptons mentioned in the above bug report, 
but fails for other cases,
like evalf( G({-2,2,-2,0},2) ).

What should be done is the following: If trailing zeros are detected in 
G_numeric, these should
be removed and the result should be returned to G_numeric. The routine 
G_numeric decides then
what to do next: either calling the convergence transformation, or Hoelder 
convolution or direct summation.
What is needed is a subroutine, which just removes trailing zeros, but 
does not perform the convergence
transformation.

With the present code the minimal modification to achieve this goal is to 
add an additional
boolean parameter flag_trailing_zeros_only to G_do_trafo (and its 
dependent sub-routines), so G_do_trafo
can be called for the removal of trailing zeros only.
The proposed patch implements this and uses G_do_trafo to remove trailing 
zeros only for the case at hand.

  Best wishes,

    Stefan
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