********> bugfix.60
Correction Author: David A. Pearlman
Correction Date: 02/24/94

Programs: GIBBS

Severity: Moderate

Problem: 

       An attempt to run a belly simulation with Gibbs can give
       erroneous results. This will only occur when one or more of 
       the following conditions have been met:

       1) The number of bonds removed from the system (non-moving parts
          of the system) is less than the number of bonds in the
          "peturbed" group.

       2) The number of angles removed from the system (non-moving parts
          of the system) is less than the number of angles in the
          "peturbed" group.

       3) The number of torsions removed from the system (non-moving parts
          of the system) is less than the number of torsions in the
          "peturbed" group.


       This bug only affects simulations run with a "belly".

Affects: 

	In all likelihood, the program would crash with a SHAKE/TORCON 
	error (if constraints were being used), or the temperature 
	behavior would be indicative of a problem.

Cause: 

	A very longstanding (since program creation) bug whereby the 
	resetting of internal coordinate pointers due to the "belly"
	was being incorrectly performed. The result is that the 
	(lambda=1) parameter pointers for internal coordinates in the
	perturbed group could be incorrectly reset.

Fix:  Make the following changes to routine SETVAR

---To routine SETVAR in file giba.f -----------------------------------------

*** OLD giba.f
--- NEW giba.f	
***************
*** 5349,5356 ****
        IX(I12+NBONH+NBONA+I-1) = IX(I18+LBONA+I-1)
        IX(I14+NBONH+NBONA+I-1) = IX(I20+LBONA+I-1)
        IX(I16+NBONH+NBONA+I-1) = IX(I22+LBONA+I-1)
-       IX(I16+NBONH+NBONA+NBPER+I-1) = IX(I22+LBONA+NBPER+I-1)
    120 CONTINUE
    140 CONTINUE
        I18 = I12+NBONH
        I20 = I14+NBONH
--- 5349,5362 ----
        IX(I12+NBONH+NBONA+I-1) = IX(I18+LBONA+I-1)
        IX(I14+NBONH+NBONA+I-1) = IX(I20+LBONA+I-1)
        IX(I16+NBONH+NBONA+I-1) = IX(I22+LBONA+I-1)
    120 CONTINUE
+ C
+ C Bugfix #60 (2/94)
+ C
+       DO 121 I = 1,NBPER
+          IX(I16+NBONH+NBONA+NBPER+I-1) = IX(I22+LBONA+NBPER+I-1)
+   121 CONTINUE
+ 
    140 CONTINUE
        I18 = I12+NBONH
        I20 = I14+NBONH
***************
*** 5379,5386 ****
        IX(I26+NTHETH+NTHETA+I-1) = IX(I34+LTHETA+I-1)
        IX(I28+NTHETH+NTHETA+I-1) = IX(I36+LTHETA+I-1)
        IX(I30+NTHETH+NTHETA+I-1) = IX(I38+LTHETA+I-1)
-       IX(I30+NTHETH+NTHETA+NGPER+I-1) = IX(I38+LTHETA+NGPER+I-1)
    220 CONTINUE
    240 CONTINUE
        I32 = I24+NTHETH
        I34 = I26+NTHETH
--- 5385,5398 ----
        IX(I26+NTHETH+NTHETA+I-1) = IX(I34+LTHETA+I-1)
        IX(I28+NTHETH+NTHETA+I-1) = IX(I36+LTHETA+I-1)
        IX(I30+NTHETH+NTHETA+I-1) = IX(I38+LTHETA+I-1)
    220 CONTINUE
+ C
+ C Bugfix #60 (2/94)
+ C
+       DO 221 I = 1,NGPER
+          IX(I30+NTHETH+NTHETA+NGPER+I-1) = IX(I38+LTHETA+NGPER+I-1)
+   221 CONTINUE
+ 
    240 CONTINUE
        I32 = I24+NTHETH
        I34 = I26+NTHETH
***************
*** 5412,5419 ****
        IX(I44+NPHIH+NPHIA+I-1) = IX(I54+LPHIA+I-1)
        IX(I46+NPHIH+NPHIA+I-1) = IX(I56+LPHIA+I-1)
        IX(I48+NPHIH+NPHIA+I-1) = IX(I58+LPHIA+I-1)
-       IX(I48+NPHIH+NPHIA+NDPER+I-1) = IX(I58+LPHIA+NDPER+I-1)
    320 CONTINUE
    340 CONTINUE
        I50 = I40+NPHIH
        I52 = I42+NPHIH
--- 5424,5437 ----
        IX(I44+NPHIH+NPHIA+I-1) = IX(I54+LPHIA+I-1)
        IX(I46+NPHIH+NPHIA+I-1) = IX(I56+LPHIA+I-1)
        IX(I48+NPHIH+NPHIA+I-1) = IX(I58+LPHIA+I-1)
    320 CONTINUE
+ C
+ C Bugfix #60 (2/94)
+ C
+       DO 321 I = 1,NDPER
+          IX(I48+NPHIH+NPHIA+NDPER+I-1) = IX(I58+LPHIA+NDPER+I-1)
+   321 CONTINUE
+ 
    340 CONTINUE
        I50 = I40+NPHIH
        I52 = I42+NPHIH
------------------------------------------------------------------------------


Temporary workarounds: 

     None.

Routines affected:

     GIBBS   Routine SETVAR in file ...amber4/src/gibbs/giba.f

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