[GiNaC-devel] [SCM] GiNaC -- a C++ library for symbolic computations branch, master, updated. release_1-4-0-433-gcda7fd3

[Richard B. Kreckel]

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- Log -----------------------------------------------------------------
commit cda7fd319d75f95fbdac21213a10a04de724d228
Author: Stefan Weinzierl <stefanw at thep.physik.uni-mainz.de>
Date:   Sun Oct 12 18:30:41 2014 +0000

    Fix log() error in multiple polylog G.
    
    Tobias Huber reported the following bug:
    > G({-0.18784426860496276*I,-0.1579006477353911*I,+0.18784426860496276*I,-0.18784426860496276*I},1);
    log_eval(): log(0)
    
    The problem is the sorting operation in G_do_trafo. This operation should
    1) put the elements in increasing order of |x|
    2) put equal elements next to each other (which then will avoid the log(0) problem).
    
    The current code fails for goal 2) if we have complex numbers of equal absolute
    value, one number occuring more than once, in an initial order like in the example
    above:
    Entries 1,3,4 of the list all have the same absolute value, entries 1 and 4 are
    equal. In the sorting operation 1 and 4 should be put next to each other.
    Previously, the sorting operation would give 2,1,3,4. What we would like to have
    is either 2,1,4,3 or 2,3,1,4. It is clear that the key for the sorting operation
    cannot be |x| alone. If |x1|=|x2| we have to use the phase as well.
    
    This patch takes the phase into account in the sorting.

commit 40b0071bbe4055bbae533634f008af38503ab696
Author: Stefan Weinzierl <stefanw at thep.physik.uni-mainz.de>
Date:   Sun Oct 12 18:24:07 2014 +0000

    Fix evaluation of some G-polylogs.
    
    This 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 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.
    
    This patch implements this and uses G_do_trafo to remove trailing zeros only for
    the case at hand.

-----------------------------------------------------------------------

Summary of changes:
 ginac/inifcns_nstdsums.cpp | 86 +++++++++++++++++++++++++++-------------------
 1 file changed, 51 insertions(+), 35 deletions(-)


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GiNaC -- a C++ library for symbolic computations