********>Bugfix 61:
Author: Ray Luo
Date: 05/2/2006
                                                                                
Programs: pbsa
                                                                                
Description: pb_force.f has a statement causing a negative number to be
             taken square root. This is not correct, but many compilers
             allow it.
                                                                                
Fix:  apply the following patch to amber8/src/pbsa/pb_force.f

------------------------------------------------------------------------------
*** pb_force.f	2005-02-07 16:56:41.000000000 -0800
--- pb_force.f	2006-05-02 17:04:03.000000000 -0700
***************
*** 2944,2950 ****
           dyij = acrd(2,jatm) - yi
           dzij = acrd(3,jatm) - zi
           d2 = dxij**2 + dyij**2 + dzij**2
!          if ( d2 >= (ri + rj)**2 ) cycle
            
           ! setting up indexes ...
            
--- 2944,2950 ----
           dyij = acrd(2,jatm) - yi
           dzij = acrd(3,jatm) - zi
           d2 = dxij**2 + dyij**2 + dzij**2
!          if ( d2 >= (ri + rj)**2 .or. d2 <= (ri - rj)**2 ) cycle
            
           ! setting up indexes ...
            
------------------------------------------------------------------------------
                                                                                
Temporary workarounds: none