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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@613 f3b2605a-c512-4ea7-a41b-209d697bcdaa

This commit is contained in:
sjplimp 2007-06-11 16:58:51 +00:00
parent fa8f1a20d2
commit 597915becb
2 changed files with 70 additions and 44 deletions
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57
doc/velocity.html
View File

@ -94,6 +94,11 @@ units; see the <A HREF = "units.html">units</A> command. The units of velocitie
coordinates depend on whether the <I>units</I> keyword is set to <I>box</I> or
<I>lattice</I>, as discussed below.
</P>
<P>For all styles, no atoms are assigned z-component velocities if the
simulation is 2d; see the <A HREF = "dimension.html">dimension</A> command.
</P>
<HR>
<P>The keyword/value option pairs are used in the following ways by the
various styles.
</P>
@ -121,30 +126,41 @@ constraints (e.g. SHAKE or rigid-body constraints), then the
appropriate fix command must be specified before the velocity command
is issued.
</P>
<P>The <I>loop</I> option is used by <I>create</I>. If loop = all, then each
processor loops over all atoms in the simulation to create velocities,
but only stores velocities for atoms it owns. This can be a slow loop
for a large simulation. It will produce the same set of velocities,
independent of the number of processors, if atoms were read from a
data file. It will not produce such independent velocities if atoms
were created using the <A HREF = "create_atoms.html">create_atoms</A> command. If
loop = local, then each processor loops over only its atoms to produce
velocities. The random number seed is adjusted to give a different
set of velocities on each processor. This is a fast loop, but will
always produce different sets of velocities when a simulation is run
on a different number of processors. If loop = geom, then each
processor loops over only its atoms. For each atom a unique random
number seed is created, based on the atom's xyz coordinates. A
velocity is generated using that seed. This is a fast loop and will
always give the same set of velocities, independent of how many
processors are used. However, the generated velocities may be more
correlated than if the <I>all</I> or <I>local</I> options are used. Note that
the <I>loop geom</I> option will not necessarily assign identical
<HR>
<P>The <I>loop</I> option is used by <I>create</I> in the following ways.
</P>
<P>If loop = all, then each processor loops over all atoms in the
simulation to create velocities, but only stores velocities for atoms
it owns. This can be a slow loop for a large simulation. If atoms
were read from a data file, the velocity assigned to a particular atom
will be the same, regardless of how many processors are being used.
This will not be the case if atoms were created using the
<A HREF = "create_atoms.html">create_atoms</A> command, since atom IDs will likely
be assigned to atoms differently.
</P>
<P>If loop = local, then each processor loops over only its atoms to
produce velocities. The random number seed is adjusted to give a
different set of velocities on each processor. This is a fast loop,
but the velocity assigned to a particular atom will depend on which
processor owns it. Thus the results will always be different when a
simulation is run on a different number of processors.
</P>
<P>If loop = geom, then each processor loops over only its atoms. For
each atom a unique random number seed is created, based on the atom's
xyz coordinates. A velocity is generated using that seed. This is a
fast loop and will always give the same set of velocities, independent
of how many processors are used. However, the generated velocities
may be more correlated than if the <I>all</I> or <I>local</I> options are used.
</P>
<P>Note that the <I>loop geom</I> option will not necessarily assign identical
velocities for two simulations run on different machines. This is
because the computations based on xyz coordinates are sensitive to
tiny differences in the double-precision value for a coordinate as
stored on a particular machine.
</P>
<HR>
<P>The <I>units</I> option is used by <I>set</I> and <I>ramp</I>. If units = box,
the velocities and coordinates specified in the velocity command are
in the standard units described by the <A HREF = "units.html">units</A> command
@ -153,9 +169,6 @@ are in units of lattice spacings per time (e.g. spacings/fmsec) and
coordinates are in lattice spacings. The <A HREF = "lattice.html">lattice</A>
command must have been previously used to define the lattice spacing.
</P>
<P>For all styles, no atoms are assigned z-component velocities if the
simulation is 2d; see the <A HREF = "dimension.html">dimension</A> command.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>

57
doc/velocity.txt
View File

@ -86,6 +86,11 @@ units; see the "units"_units.html command. The units of velocities and
coordinates depend on whether the {units} keyword is set to {box} or
{lattice}, as discussed below.
For all styles, no atoms are assigned z-component velocities if the
simulation is 2d; see the "dimension"_dimension.html command.
:line
The keyword/value option pairs are used in the following ways by the
various styles.
@ -113,30 +118,41 @@ constraints (e.g. SHAKE or rigid-body constraints), then the
appropriate fix command must be specified before the velocity command
is issued.
The {loop} option is used by {create}. If loop = all, then each
processor loops over all atoms in the simulation to create velocities,
but only stores velocities for atoms it owns. This can be a slow loop
for a large simulation. It will produce the same set of velocities,
independent of the number of processors, if atoms were read from a
data file. It will not produce such independent velocities if atoms
were created using the "create_atoms"_create_atoms.html command. If
loop = local, then each processor loops over only its atoms to produce
velocities. The random number seed is adjusted to give a different
set of velocities on each processor. This is a fast loop, but will
always produce different sets of velocities when a simulation is run
on a different number of processors. If loop = geom, then each
processor loops over only its atoms. For each atom a unique random
number seed is created, based on the atom's xyz coordinates. A
velocity is generated using that seed. This is a fast loop and will
always give the same set of velocities, independent of how many
processors are used. However, the generated velocities may be more
correlated than if the {all} or {local} options are used. Note that
the {loop geom} option will not necessarily assign identical
:line
The {loop} option is used by {create} in the following ways.
If loop = all, then each processor loops over all atoms in the
simulation to create velocities, but only stores velocities for atoms
it owns. This can be a slow loop for a large simulation. If atoms
were read from a data file, the velocity assigned to a particular atom
will be the same, regardless of how many processors are being used.
This will not be the case if atoms were created using the
"create_atoms"_create_atoms.html command, since atom IDs will likely
be assigned to atoms differently.
If loop = local, then each processor loops over only its atoms to
produce velocities. The random number seed is adjusted to give a
different set of velocities on each processor. This is a fast loop,
but the velocity assigned to a particular atom will depend on which
processor owns it. Thus the results will always be different when a
simulation is run on a different number of processors.
If loop = geom, then each processor loops over only its atoms. For
each atom a unique random number seed is created, based on the atom's
xyz coordinates. A velocity is generated using that seed. This is a
fast loop and will always give the same set of velocities, independent
of how many processors are used. However, the generated velocities
may be more correlated than if the {all} or {local} options are used.
Note that the {loop geom} option will not necessarily assign identical
velocities for two simulations run on different machines. This is
because the computations based on xyz coordinates are sensitive to
tiny differences in the double-precision value for a coordinate as
stored on a particular machine.
:line
The {units} option is used by {set} and {ramp}. If units = box,
the velocities and coordinates specified in the velocity command are
in the standard units described by the "units"_units.html command
@ -145,9 +161,6 @@ are in units of lattice spacings per time (e.g. spacings/fmsec) and
coordinates are in lattice spacings. The "lattice"_lattice.html
command must have been previously used to define the lattice spacing.
For all styles, no atoms are assigned z-component velocities if the
simulation is 2d; see the "dimension"_dimension.html command.
[Restrictions:] none
[Related commands:]