[Ifeffit] FEFF report: Hard tests failed in fovrg.

Wed Aug 7 13:29:05 CDT 2013

Dear Ifeffit community,

a short reaction from the FEFFgroup.

1/  It's true that we don't follow up on the ifeffit ML 100%.  Important
issues usually do get through to us.  We highly value the ifeffit
community.  We can also be contacted directly for problems that are FEFF
related rather than iFEFFit related (
contact<http://www.feffproject.org/feffproject-contact.html> ).
 We'll likely ask you for the feff.inp file that generates the problem.

2/  We're glad that FEFF6 is so successful.  Meanwhile FEFF6 is about as
old as Windows95, and development is now focused on
FEFF9<http://www.feffproject.org/feffproject-feff.html>,
which has 15-20 years of improvements over FEFF6.  It's a big improvement
for anyone running FEFF calculations.  It costs $500, or $250 upgrade from
any paid version of FEFF.

3/  The OP posted 5 input files.  4 of these run without problems in FEFF9.
 The last has I atoms (Z=53) at a spacing of 0.8A, and doesn't run out of
the box.  I expect the same result from FEFF8.

4/  There has been some effort to bring a "FEFF9lite" to the analysis
codes, analogous to the FEFF6lite discussed here.  We would be very happy
to see that effort succeed.

5/  FWIW the fovrg routine was retired in 1996 and replaced by a
relativistic version called "dfovrg".  The "hard error" does not exist
anymore.

6/  We're a small team; we apologize for all the 'bothering' we don't get
around to.  We do care about supporting our users and put a lot of energy
into support.  Please reach out ot us when you need us.

Cheers from Seattle,

Kevin Jorissen

PS I posted a while back about a problem with JFEFF and Java updates but
I'm not sure the message made it through: I asked the mod, but no reply.  I
hope this msg makes it :).

On Wed, Aug 7, 2013 at 8:24 AM, Bruce Ravel <bravel at bnl.gov> wrote:

> On 08/06/2013 11:55 AM, Naumova, Maria wrote:
>
>> May I use this FEFF calculation as a valid base for future fit? Or
>> this error means that FEFF doesn't work correct and I can't rely on
>> its output? If the phase-shift program failed to converge does it
>> mean that it could stop in some completely unrealistic result?
>>
>
>
> Maria,
>
> You are correct that the version of Feff6 that we are allowed to give
> away for free reliably complains about failing something called a
> "hard test".  This is some kind of convergence test on the computation
> of the muffin tin potential.
>
> The test is made in the lines just prior to this:
>
> https://github.com/newville/**ifeffit/blob/master/src/feff6/**fovrg.f#L158<https://github.com/newville/ifeffit/blob/master/src/feff6/fovrg.f#L158>
>
>
> The error is reported here:
>
> https://github.com/newville/**ifeffit/blob/master/src/feff6/**phase.f#L127<https://github.com/newville/ifeffit/blob/master/src/feff6/phase.f#L127>
>
>
> If you can make heads to tails out of the calculation in fovrg.f, you
> are vastly smarter than me, vastly more patient than me, or both!
>
> I have 2 comments on the main point of your post:
>
>  1. As you noted, this question has been asked many times before.  Not
>     once has anyone from the Feff project (i.e. anyone who might
>     actually have a working knowledge of that bit of code) bothered to
>     comment.  It would be lovely to hear from one of them.
>
>  2. This very version of Feff has been included with Ifeffit and with
>     the packages I build for my software for years.  Over a decade, in
>     fact.  In that time, Feff, Ifeffit, and my software have been used
>     for defensible data analysis thousands of times and by hundreds of
>     practitioners.
>
>     That does not mean that any part of the software stack is actually
>     correct.  But it does mean that lots of article writers and lots
>     of article reviewers have accepted the results coming from this
>     stack of software.
>
>     That does not mean that you should accept it.  Quite the contrary
>     -- you would be wise to question every part of the software stack.
>     You may even find that you will need to discard any or all parts
>     of that software stack and replace them with something you trust
>     more -- perhaps even with something that you, yourself have
>     written.
>
> To summarize, I am saying the same thing I have said in the past.  I
> don't understand the code that generates that message.  No one from
> the Feff project has ever bothered weighing in on what it means.  No
> one has demonstrated that it represents an actionable problem.  The
> codes which use Feff have been in use for years to produce defensible
> science.
>
> So, in conclusion, what should you do?  I have no idea.  My advice is
> to continue using the software, but my advice may not be any more
> reliable than the software itself.
>
> I hope that helps.  Probably doesn't, but it's the best I can do.
> B
>
>
> --
>  Bruce Ravel  ------------------------------**------ bravel at bnl.gov
>
>  National Institute of Standards and Technology
>  Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
>  Building 535A
>  Upton NY, 11973
>
>  Homepage:    http://xafs.org/BruceRavel
>  Software:    https://github.com/bruceravel
> ______________________________**_________________
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