AMBER Archive (2006)

Subject: AMBER: Different result for serial and parallel sander with IREST=1 (AMBER 8) !

From: Pradipta Bandyopadhyay (pradipta_at_iitg.ernet.in)
Date: Mon Apr 03 2006 - 00:23:26 CDT

I compiled AMBER 8 in both in serial and parallel mode. The machine is
dual processor (dual core) Xeon - OS - Red Hat Linux

uname -a gives

Linux localhost.localdomain 2.4.21-4.ELsmp #1 SMP Fri Oct 3 17:52:56 EDT
2003 i686 i686 i386 GNU/Linux

I applied all bug fixes (using bugfix.all).

The sander test runs were all passed.

When I tested the serial and parallel for a longer job with the following
input file:

----------------------------------------------
 &cntrl
   IREST = 1,
   NTX = 5,
   NTB = 2,
   NTT = 1, TAUTP = 1.0,
   TEMPI = 300.0,
   TEMP0 = 300.0,
   NTP = 1,
   NSTLIM= 1000, DT = .002,
   NTC = 2,
   NTF = 2,
   NTPR = 25, NTWX = 400,NTWV=1000,
 &end
---------------------------------------------------

upto 400 steps the results are identical (i.e. if we consider 4 digits
after decimal - as sander prints). However, after that the two simulations
start to diverge slowly.

-------------------------------------------------------------------------
For PARALLEL

NSTEP = 400 TIME(PS) = 2337.800 TEMP(K) = 301.88 PRESS =
-146.6
 Etot = -69050.9144 EKtot = 17607.3844 EPtot =
-86658.2987

NSTEP = 425 TIME(PS) = 2337.850 TEMP(K) = 299.56 PRESS =
-121.8
 Etot = -69048.6159 EKtot = 17471.7576 EPtot =
-86520.3735

......................................................
..............................................

NSTEP = 1000 TIME(PS) = 2339.000 TEMP(K) = 298.45 PRESS =
-103.1
 Etot = -69039.0240 EKtot = 17407.0499 EPtot =
-86446.0739

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

For SERIAL

NSTEP = 400 TIME(PS) = 2337.800 TEMP(K) = 301.88 PRESS =
-146.6
 Etot = -69050.9144 EKtot = 17607.3844 EPtot =
-86658.2987

NSTEP = 425 TIME(PS) = 2337.850 TEMP(K) = 299.56 PRESS =
-121.8
 Etot = -69048.6160 EKtot = 17471.7575 EPtot =
-86520.3735

..........................
.......................
NSTEP = 1000 TIME(PS) = 2339.000 TEMP(K) = 300.35 PRESS =
-33.4
 Etot = -69044.6579 EKtot = 17518.1645 EPtot =
-86562.8224
----------------------------------------------------------------

Has anyone experienced the same?

Thanks,

     Pradipta

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