Problems with using region block with dynamic group

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1

Hi,

Today I tried to use region block with dynamic groups, while for region sphere it works, by only changing region sphere to region block, it failed with

ERROR: Expected floating point parameter in input script or data file (…/region_block.cpp:45)

, I did a rough look at the source code of region_sphere.cpp and region_block.cpp, it seems that using variables in terms of v_ is not enabled in region block yet. To me this is necessary for using region with dynamic group as ${v} will not be updated, resulting in a static region.

Am i right?

the input files are attached, it is based on examples/meam, with few modifications according to http://lammps.sandia.gov/doc/group.html.

Best

Ming

dg-test.tar.gz (5.46 KB)

2

Hi,

Today I tried to use region block with dynamic groups, while for region
sphere it works, by only changing region sphere to region block, it failed
with

ERROR: Expected floating point parameter in input script or data file
(../region_block.cpp:45)

, I did a rough look at the source code of region_sphere.cpp and
region_block.cpp, it seems that using variables in terms of v_ is not
enabled in region block yet. To me this is necessary for using region with
dynamic group as ${v} will not be updated, resulting in a static region.
Am i right?

​yes and no. the problem is not with the dynamic group per se, since you
can still have the group definition re-evaluated dynamically during the run
according to the region. so that​ feature is working as advertised.
however, you correctly noticed that block style regions cannot be based on
a variable evaluated during the run. so strictly speaking, it is a dynamic
region issue, but it can be solved with some programming in the block style
region code.

axel.

3

I did a rough look at the source code of region_sphere.cpp and region_block.cpp, it seems that using variables in terms of >v_ is not enabled in region block yet. To me this is necessary for using region with dynamic group as ${v} will not be >updated, resulting in a static region.

Am i right?

yes. In fact, no command in LAMMPS will allow a variable name (v_name) to
be used as a numeric input, unless the doc page explicitly says that
parameter can be specified as a variable.

I mention this b/c some users (not you) think that it is OK to put
v_name anywhere they like in their input script and expect it to work.

That is not the case.

Steve

4

Hi, Axel, and Steve,

Thanks for this explanation :slight_smile:

best

Ming