[PATCH] extension to pair_dpd

I would like to propose an extension to pair_dpd style. It is trivial and
adds two parameters to the formula for forces.

I took it from [1] with a change in notation m_{lammps}: s_{fan}/2
to have Groot [2] formulation for m=1.

Please consider patch in the attachments, a draft of new
documentation [3] (also in the patch), a test case I add to the patch:
examples/dpd-tests. The test compares one component of the force (and
the stress) from lammps with an output of a small script.

1. X. Fan, N. Phan-Thien, S. Chen, X. Wu, and T. Y. Ng, Phys. Fluids
   18, 063102 (2006) http://dx.doi.org/10.1063/1.2206595
2. R. D. Groot and P. B. Warren, J Chem Phys, 107, 4423-35 (1997)
3. http://slitvinov.github.com/lammps/pair_dpd/
4. Current pair_dpd documentation

0001-Modify-pair_dpd-style-extended-dpd-formulation-adds-.patch (56.9 KB)

Add a driver script to the test.

0002-Add-a-driver-script-for-the-dpd-test.patch (809 Bytes)