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[ESPResSo-users] OIF, deviation in "origin"-command

From: Wink, Markus
Subject: [ESPResSo-users] OIF, deviation in "origin"-command
Date: Tue, 25 Feb 2014 14:02:36 +0000

Dear all,


I have noticed a quite strange behavior in the command “origin” for the OIF-implementation. Probably somebody can help me out with that. In my script, I have put a sphere in a channel at a specific position. Afterwards I wanted to check, which result the command “origin” gives. The interesting parts of my scripts are:


oif_create_template template-id 0 nodes-file $fileNodes triangles-file $fileTriangles ks 10 kb 10 kv 50

oif_add_object object-id 1 template-id 0 origin 15 15 15 rotate 0 0 0 part-type 1 mass 1

set x [oif_object_analyze object-id 0 origin]

puts $x


So I put the object with its origin @ 15 15 15; command “origin” prints out: 15.008655470737903 15.02980503816793 14.995383511450385

No integration of the system has be done so far.


I can think of two reasons for the deviation:

1)    The source code is correct and the deviation results because of rounding errors

2)    The template I have used (I used the sphere_nodes/triangles.dat found on git hub) is somehow not correct. Actually, I have noticed, that the points given do not exactly fulfill the relation for a sphere (x^2+y^2+z^2=r^2). So it could be that the deviation origins from that artefact.

3)    The calculations performed by the command “origin” has some error. Unfortunately, I could not locate, where the calculation is performed in the source code.


Does anyone have a clue?




Markus Wink

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