amber-developers: current status of ncsu and rem code

From: David A. Case <case.scripps.edu>
Date: Fri, 21 Dec 2007 10:17:34 -0800

I've checked in changes from Volodymyr, and for me, both serial and parallel
codes now compile. But I had to make some tweaks, and there seems to be
cross-purposes about the "rem" variable:

In multisander (and elsewhere in Dan's code I think), rem gets set and passed
around only when MPI is set. It's not clear to me what happens when MPI
is not set (it's in the code: I just haven't studied carefully enough to
figure it out.) There clearly seem to be places where it is assumed that rem
and remd variables are only available under MPI.

There is a comment in remd.f that indicates that some variables might be
available without MPI, but I'm not yet convinced that this is consistently
handled.

The force.f routine uses the rem variable when LES is turned on, even if MPI
is not set. I put in a declaration just to make the code compile, but this
needs to be looked at -- if the intent is to disable simulatneous rem and LES
(?), that should be done once (presumably in mdread.f) and not everywhere
inside force.f. If there is some other intent, things should be commented and
fixed.

The ncsu stuff uses the "rem" variable, but in serial mode this is probably
not available. I haven't taken the time to try to grok the connection between
remd and ncsu, since I figure others understand the code much better than I
do.

My bias (based on what I know now): replica exchange seems to require MPI, and
we should not try to be using those variables in serial code. But I'm open
to alternatives. We certainly could have an "rem" variable that was set to 0
(but still visible) in serial code, [somewhat like we define master=.true.
in serial code so that code like "if(master)" will work in both serial and
parallel.]

So, please look at what is there, and make appropriate fixes.

...thanks!...dave

-- 
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David A. Case                     |  e-mail:      case.scripps.edu
Dept. of Molecular Biology, TPC15 |  fax:          +1-858-784-8896
The Scripps Research Institute    |  phone:        +1-858-784-9768
10550 N. Torrey Pines Rd.         |  skype:                 dacase
La Jolla CA 92037  USA            |    http://www.scripps.edu/case
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Received on Sun Dec 23 2007 - 06:07:33 PST
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