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[ESPResSo] Local stress tensor/Multibody interaction and A bug in tensor

From: Zunjing Wang
Subject: [ESPResSo] Local stress tensor/Multibody interaction and A bug in tensor distribute
Date: Tue, 16 Jun 2009 08:20:13 -0400
User-agent: Microsoft-Entourage/

Hi, all,

Here I have several questions on command "analyze local_stress_tensor" or "
analyze stress_tensor" for computing local/total stress tensor of an
non-isotropic system, for example, a membrane.

1) Checking with the newest released version Espresso-2.1.2j, I found that
it does not include any 3-body or higher-order interactions, eg. Angle
bending, Dihedrals. Has any Espresso developer ever coded this part? If not,
then when involving any three-body interactions, how reliable about the
results of stress tensor with current Espresso?

2) Another question is about a bug in source code:
IN FILE:   pressure.c
FUNCTION:  int distribute_tensors(DoubleList *TensorInBin, double *force,
int bins[3], double range_start[3], double range[3], double pos1[3], double
LINE 757-762:
if (calclength - length >0.0000000001) {
      char *errtxt = runtime_error(128 + 3*TCL_INTEGER_SPACE);
      ERROR_SPRINTF(errtxt, "{%d: analyze stess_profile: bug in distribute
tensor code - calclength is %e and length is %e calclength-length is %e,
counter is %d}",this_node,calclength,length,calclength-length, counter);
      return 0;
Does anyone know how this value "0.0000000001" was decided? Will it be
effected by compiler or machine?

Thanks in advance for any possible help,

Zun-Jing WANG, Ph.D.
Dept. of Physics                      ++1-412-268-2771 (office)
Carnegie Mellon University            ++1-412-681-0648 (fax)
5000 Forbes Avenue                    ++1-412-268-2740 (Donna Thomas)
Pittsburgh, PA 15213                  address@hidden


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