[Wien] Bug alert for the mixer

[Laurence Marks]

At high optimization levels (-O2 -ipo) which are possible although not
those recommended, it is possible that the mixer will switch
unintentionally to "Good Broyden" mode. Due to the trust region control
this will probably still converge in most cases, but is less stable and
less desirable. A test of this is to do "grep :RANK *.scfm". If two lines
with :RANK appear, e.g.

:RANK :  ACTIVE  11.98/12 =  99.81 % ; YY RANK  11.98/12 =  99.81 %
:RANK :  ACTIVE  11.98/12 =  99.81 % ; YY RANK

then the bug is present. To cure it in SRC_mixer change the line in
SRC_mixer/module.F so that in the module VerNew the variables SMode and
YMode are initialized to false, i.e.

  Logical               :: SMode=.false., YMode=.false., KillNPC = .false.

To repeat, this appears to only be an issue with high optimization levels
of the latest ifort.

-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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