[ESPResSo-devel] One question about MPI

[Ivan Cimrak]

Hi,

I tested some MPI code (see the script below) and found out the following:

Define simulation box with dimensions 20x20x20. Define 8 particles 
located in the vertices of a smaller cube with an edge of length 2. The 
smaller cube is located such that its center has coordinates 10 10 10 
and the smaller cube's faces are parallel to the faces of the simulation 
box.

Define 12 bonds between the particles along the edges of the cube, e.g. 
with fene interactions.
Then run the parallel code on 8 precessors. The simulation box will be 
divided into 8 subcubes with dimension 10x10x10. Unfortunately, in each 
of these subcubes you have just one particle and you get the error

background_errors 0 {083 bond broken between particles 0 and 1 
(particles not stored on the same node)} etc....

How can I avoid these errors?  Can anybody give some explanation?

One can play with variables A and B by decreasing the size of smaller 
cube and once the smaller cube has the edge smaller than 1, everything 
is fine.

Thanks,

Ivan

Script:
setmd time_step 0.001
setmd skin 0.2

thermostat off

setmd box_l 20 20 20

set A 9
set B 11
part 0 pos $A $A $A type 0
part 1 pos $B $A $A type 0
part 2 pos $B $B $A type 0
part 3 pos $A $B $A type 0
part 4 pos $A $A $B type 0
part 5 pos $B $A $B type 0
part 6 pos $B $B $B type 0
part 7 pos $A $B $B type 0

inter 0 fene 10.0 1.0

part 0 bond 0 1
part 1 bond 0 2
part 2 bond 0 3
part 3 bond 0 0
part 4 bond 0 5
part 5 bond 0 6
part 6 bond 0 7
part 7 bond 0 4
part 0 bond 0 4
part 1 bond 0 5
part 2 bond 0 6
part 3 bond 0 7

integrate 1