********> bugfix.66
Correction Author: David A. Pearlman
Correction Date: 09/19/94

Programs: Gibbs

Severity: minor

Problem: 

       When running a free energy simulation with ICORC = 1 (constraint
       contributions included), it is possible that an attempt would
       be made to write several undefined variables to the restart file.
       Although these variables are not important (and not used)
       in any case where they might be undefined, on some computers
       the undefined variables would be set to large values, which
       would in turn result an overflow of the corresponding fields
       in the restart file (e.g. "stars"). A subsequent attempt to
       read the restart file for a restart run (IREST=1) might then
       fail.

       The undefined variables would appear in the second and third
       lines following the "CONSTRAINTS" flag in the restart file, 
       as in this example: 

CONSTRAINTS
    1    0    0    0    0    0    0    1    0
*******************************************************************************
***********************************************************************
 2306.74    -2306.74
-1.36445     1.36445
0.000000E+00

Affects: 

       An attempt to read the restart file as the "coordinate" file
       in a subsequent restart run (IREST=1) might fail with an
       error about improper format information in the restart file.
 
       Note that in NO CASE would the energies reported (or trajectories
       calculated) by the program be incorrect. Also note that on some
       computers, the uninitialized variables would get set to
       values that fall within range of the format used to write them out,
       and no problem would be noticed by the user.

Cause: 

       A small bug in the routine that writes the values would
       allow the possibility of writing the values before they
       were defined.

Fix:  Make the following changes to routine CCPRT in gibbs

---gibbs: Module connrg.f  -----------------------------

*** OLD connrg.f
--- NEW connrg.f
***************
*** 2722,2728 ****
        DATA LASTCL/0/
        SAVE LASTCL
  C
!       IF (IONCE.NE.10 .AND. INDEX.LE.1) THEN
            IONCE = 10
            ICALLS = 0
            NSTEP0 = 0
--- 2722,2728 ----
        DATA LASTCL/0/
        SAVE LASTCL
  C
!       IF (IONCE.NE.10) THEN
            IONCE = 10
            ICALLS = 0
            NSTEP0 = 0
------------------------------------------------------------------------------

Temporary workarounds: 

     If you encounter this problem. You may simply remove the "CONSTRAINTS"
     flag line, and the (precisely) _six_ lines following it from the
     restart file. A subsequent restart run using this file will report
     the following message, which you can safely ignore:

     "WARNING: Constraint information could not be found in restart file"

Routines affected:

     GIBBS file ...amber4/src/gibbs/connrg.f        


--