********> bugfix.51
Author:   Carlos Simmerling
Date:     10/24/95

Programs: Sander

Severity: Moderate

Problem:  When NTT<0, the random number generator is being reset
          every time velocities are reassigned, leading to fixed
          velocities and system blowup when resetting results
          from temperature difference from the reference exceeding 
          DTEMP.

Cause:    Random number seeding was done in the velocity setting
          routine instead of at the beginning of program; this
          was ok until the NTT<0 options were added in 4.1.


Fix:  Make the following changes to dynlib.f and sander.f:
------------------------------------------------------------------------
*** OLD dynlib.f
--- NEW dynlib.f
***************
*** 857,864
  c     sets up initial velocities.
  c     Mods for Rev A by gls:
  c
- c     - added call to generic random number initializer.  previous
- c       incarnations of Amber simply ignored the seed on most systems.
  c     - cpp selectable single/double prec.
  c     - changed to DP constants
  #ifdef DPREC 

--- 857,862 -----
  c     sets up initial velocities.
  c     Mods for Rev A by gls:
  c
  c     - cpp selectable single/double prec.
  c     - changed to DP constants
  #ifdef DPREC 
***************
*** 867,873
        DIMENSION X(*),V(*),WINV(*),F(*)
  C
        NR3 = 3*NR
-       ISEED = IG
        IF(NTU.NE.2 ) GOTO 131
        CRX = 0.1d0
        DO 110 I = 1,NR3+iscale

--- 865,870 -----
        DIMENSION X(*),V(*),WINV(*),F(*)
  C
        NR3 = 3*NR
        IF(NTU.NE.2 ) GOTO 131
        CRX = 0.1d0
        DO 110 I = 1,NR3+iscale
***************
*** 892,901
  C           WHEN REQUIRED -----
  C
    141 IF(TEMPI.LT.1.d-6) GOTO 171
- c
- c     --- seed the random number generator ---
- c
-       call amrset(iseed)
        BOLTZ = 8.31441d-3
        IF(NTU.EQ.1) BOLTZ = BOLTZ/4.184d0
        BOLTZ = BOLTZ*TEMPI

--- 889,894 -----
  C           WHEN REQUIRED -----
  C
    141 IF(TEMPI.LT.1.d-6) GOTO 171
        BOLTZ = 8.31441d-3
        IF(NTU.EQ.1) BOLTZ = BOLTZ/4.184d0
        BOLTZ = BOLTZ*TEMPI
------------------------------------------------------------------------
*** OLD sander.f
--- NEW sander.f
***************
*** 379,384
        NR3 = 3*NR
        BELLY = IBELLY.GT.0
  c
        if (nbit .lt. 32 .and. nr .gt. 32767) then
             write(6, *) '  Too many atoms for 16 bit pairlist -'
             write(6, *) '    Recompile without ISTAR2'

--- 379,388 -----
        NR3 = 3*NR
        BELLY = IBELLY.GT.0
  c
+ c     --- seed the random number generator ---
+ c
+       call amrset(ig)
+ c
        if (nbit .lt. 32 .and. nr .gt. 32767) then
             write(6, *) '  Too many atoms for 16 bit pairlist -'
             write(6, *) '    Recompile without ISTAR2'
------------------------------------------------------------------------

Temporary workarounds: None.

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