Is it a bug? TCL Script may Lead to Overflow

From: Fred (Rui FENG) (fengruifree_at_gmail.com)
Date: Sat Nov 07 2009 - 03:09:28 CST

Hi All,

I found that if TCL script lines are more than a certain value (maybe
35 to 40) in the parameter file, some variables will overflow and
impact the variable (at least) called "zeroMomentumAlt". For example,
the code below is to add a gradient force. To reproduce this error,
just append the code below to the popular ApoA1 parameter file which
can be download here:
http://www.ks.uiuc.edu/Research/namd/utilities/apoa1/apoa1.namd

The variable "zeroMomentumAlt" is only set in SimParameters.C and
referenced by Sequencer.C. Its value can be printed in Controller.C.

For example, in receivePressure function you can write: iout <<
"zeroMomentumAlt = " << simParameters->zeroMomentumAlt << "\n" <<
endi;

You will find that the value will be changed from 0 (false) to a large
int number.

NAMD 2.7b1 and 2.6 have this problem. TCL version is the latest 8.5.7
(the 8.4.14 is also tried).

My computing and compiling environment: Blue Gene/L, 512/1024 nodes,
Co-processor/Virtual node mode.

My output:
Step = 1 zeroMomentumAlt = 1702109286 zeroMomentum = 0
Step = 2 zeroMomentumAlt = 1702109286 zeroMomentum = 0
Step = 3 zeroMomentumAlt = 1702109286 zeroMomentum = 0
Step = 4 zeroMomentumAlt = 1702109286 zeroMomentum = 0
Step = 5 zeroMomentumAlt = 1702109286 zeroMomentum = 0
.......................

But if you delete some "elseif" in the tcl script and only keep two or
three of them, the problem disappeared!

I guess when NAMD parses the TCL script which is more than a certain
value, some variables overflow and impact the memory that saves
"zeroMomentumAlt".

Could you help me to check it out? Thanks!

Regards,
Fred

=============== THE CODE ================
wrapall on

tclBC on
tclBCScript {
  wrapmode cell

  proc calcforces {step unique frc bndry bndrymax numwall} {
    while {[nextatom]} {
      set id [getid]
      if {$id <= $numwall} {
        dropatom
        continue
      }
      set vec [getcoord]
      foreach {x y z} $vec {break}
      if { $step > 0 } {
        if {$x > -50.0 && $x < -45.0} {
          set f "1.000 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -45.0 && $x < -40.0} {
          set f "0.999 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -40.0 && $x < -35.0} {
          set f "0.998 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -35.0 && $x < -30.0} {
          set f "0.997 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -30.0 && $x < -25.0} {
          set f "0.996 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -25.0 && $x < -20.0} {
          set f "0.995 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -20.0 && $x < -15.0} {
          set f "0.994 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -15.0 && $x < -10.0} {
          set f "0.993 0. 0."
          addforce [vecscale $frc $f]
        } elseif {$x >= -10.0 && $x < -5.0} {
          set f "0.992 0. 0."
          addforce [vecscale $frc $f]
        } else {
          set f "0.991 0. 0."
          addforce [vecscale $frc $f]
        }
      }
    }
  }
}

tclBCArgs {0.01 -54.0 54.0 0}

=================END=================

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