forked from lijiext/lammps
git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@11459 f3b2605a-c512-4ea7-a41b-209d697bcdaa
This commit is contained in:
sjplimp
parent
e3979f6143
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<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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</CENTER>
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<HR>
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<H3>fix vector command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID vector Nevery value1 value2 ...
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>ave/time = style name of this fix command
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<LI>Nevery = use input values every this many timesteps
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<LI>one or more input values can be listed
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<LI>value = c_ID, c_ID[N], f_ID, f_ID[N], v_name
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<PRE> c_ID = global scalar calculated by a compute with ID
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c_ID[I] = Ith component of global vector calculated by a compute with ID
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f_ID = global scalar calculated by a fix with ID
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f_ID[I] = Ith component of global vector calculated by a fix with ID
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v_name = global value calculated by an equal-style variable with name
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 1 all vector 100 c_myTemp
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fix 1 all vector 5 c_myTemp v_integral
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Use one or more global values as inputs every few timesteps, and
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simply store them. For a single specified value, the values are
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stored as a global vector of growing length For multiple specified
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values, they are stored as rows in a global array, whose number of
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rows is growing. The resulting vector or array can be used by other
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<A HREF = "Section_howto.html#howto_15">output commands</A>.
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</P>
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<P>One way to to use this command is to accumulate a vector that is
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time-integrated using the <A HREF = "variable.html">variable trap()</A> function.
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For example the velocity auto-correlation function (VACF) can be
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time-integrated, to yield a diffusion coefficient, as follows:
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</P>
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<PRE>compute 2 all vacf
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fix 5 all vector 1 c_2<B>4</B>
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variable diff equal dt*trap(f_5)
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thermo_style custom step v_diff
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</PRE>
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<P>The group specified with this command is ignored. However, note that
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specified values may represent calculations performed by computes and
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fixes which store their own "group" definitions.
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</P>
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<P>Each listed value can be the result of a <A HREF = "compute.html">compute</A> or
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<A HREF = "fix.html">fix</A> or the evaluation of an equal-style
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<A HREF = "variable.html">variable</A>. In each case, the compute, fix, or variable
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must produce a global quantity, not a per-atom or local quantity.
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And the global quantity must be a scalar, not a vector or array.
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</P>
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<P><A HREF = "compute.html">Computes</A> that produce global quantities are those which
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do not have the word <I>atom</I> in their style name. Only a few
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<A HREF = "fix.html">fixes</A> produce global quantities. See the doc pages for
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individual fixes for info on which ones produce such values.
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<A HREF = "variable.html">Variables</A> of style <I>equal</I> are the only ones that can
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be used with this fix. Variables of style <I>atom</I> cannot be used,
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since they produce per-atom values.
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</P>
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<P>The <I>Nevery</I> argument specifies on what timesteps the input values
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will be used in order to be stored. Only timesteps that a multiple
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of <I>Nevery</I>, including timestep 0, will contribute values.
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</P>
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<HR>
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<P>If a value begins with "c_", a compute ID must follow which has been
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previously defined in the input script. If no bracketed term is
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appended, the global scalar calculated by the compute is used. If a
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bracketed term is appended, the Ith element of the global vector
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calculated by the compute is used.
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</P>
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<P>Note that there is a <A HREF = "compute_reduce.html">compute reduce</A> command
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which can sum per-atom quantities into a global scalar or vector which
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can thus be accessed by fix vector. Or it can be a compute defined
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not in your input script, but by <A HREF = "thermo_style.html">thermodynamic
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output</A> or other fixes such as <A HREF = "fix_nh.html">fix nvt</A>
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or <A HREF = "fix_temp_rescale.html">fix temp/rescale</A>. See the doc pages for
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these commands which give the IDs of these computes. Users can also
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write code for their own compute styles and <A HREF = "Section_modify.html">add them to
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LAMMPS</A>.
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</P>
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<P>If a value begins with "f_", a fix ID must follow which has been
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previously defined in the input script. If no bracketed term is
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appended, the global scalar calculated by the fix is used. If a
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bracketed term is appended, the Ith element of the global vector
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calculated by the fix is used.
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</P>
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<P>Note that some fixes only produce their values on certain timesteps,
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which must be compatible with <I>Nevery</I>, else an error will result.
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Users can also write code for their own fix styles and <A HREF = "Section_modify.html">add them to
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LAMMPS</A>.
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</P>
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<P>If a value begins with "v_", a variable name must follow which has
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been previously defined in the input script. Only equal-style
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variables can be referenced. See the <A HREF = "variable.html">variable</A> command
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for details. Note that variables of style <I>equal</I> define a formula
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which can reference individual atom properties or thermodynamic
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keywords, or they can invoke other computes, fixes, or variables when
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they are evaluated, so this is a very general means of specifying
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quantities to be stored by fix vector.
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</P>
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<HR>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix.
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</P>
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<P>This fix produces a global vector or global array which can be
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accessed by various <A HREF = "Section_howto.html#howto_15">output commands</A>.
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The values can only be accessed on timesteps that are multiples of
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<I>Nevery</I>.
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</P>
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<P>A vector is produced if only a single input value is specified.
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An array is produced if multiple input values are specified.
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The length of the vector or the number of rows in the array grows
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by 1 every <I>Nevery</I> timesteps.
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</P>
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<P>If the fix prouduces a vector, then the entire vector will be either
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"intensive" or "extensive", depending on whether the values stored in
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the vector are "intensive" or "extensive". If the fix produces an
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array, then all elements in the array must be the same, either
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"intensive" or "extensive". If a compute or fix provides the value
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stored, then the compute or fix determines whether the value is
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intensive or extensive; see the doc page for that compute or fix for
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further info. Values produced by a variable are treated as intensive.
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</P>
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<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
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minimization</A>.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute.html">compute</A>, <A HREF = "variable.html">variable</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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@ -0,0 +1,148 @@
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix vector command :h3
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[Syntax:]
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fix ID group-ID vector Nevery value1 value2 ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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ave/time = style name of this fix command :l
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Nevery = use input values every this many timesteps :l
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one or more input values can be listed :l
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value = c_ID, c_ID\[N\], f_ID, f_ID\[N\], v_name :l
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c_ID = global scalar calculated by a compute with ID
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c_ID\[I\] = Ith component of global vector calculated by a compute with ID
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f_ID = global scalar calculated by a fix with ID
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f_ID\[I\] = Ith component of global vector calculated by a fix with ID
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v_name = global value calculated by an equal-style variable with name :pre
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:ule
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[Examples:]
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fix 1 all vector 100 c_myTemp
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fix 1 all vector 5 c_myTemp v_integral :pre
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|
[Description:]
|
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|
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|
Use one or more global values as inputs every few timesteps, and
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|
simply store them. For a single specified value, the values are
|
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stored as a global vector of growing length For multiple specified
|
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|
values, they are stored as rows in a global array, whose number of
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|
rows is growing. The resulting vector or array can be used by other
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|
"output commands"_Section_howto.html#howto_15.
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|
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One way to to use this command is to accumulate a vector that is
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time-integrated using the "variable trap()"_variable.html function.
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For example the velocity auto-correlation function (VACF) can be
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|
time-integrated, to yield a diffusion coefficient, as follows:
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|
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compute 2 all vacf
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fix 5 all vector 1 c_2[4]
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|
variable diff equal dt*trap(f_5)
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|
thermo_style custom step v_diff :pre
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|
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|
The group specified with this command is ignored. However, note that
|
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|
specified values may represent calculations performed by computes and
|
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|
fixes which store their own "group" definitions.
|
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|
|
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|
Each listed value can be the result of a "compute"_compute.html or
|
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|
"fix"_fix.html or the evaluation of an equal-style
|
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|
"variable"_variable.html. In each case, the compute, fix, or variable
|
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|
must produce a global quantity, not a per-atom or local quantity.
|
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|
And the global quantity must be a scalar, not a vector or array.
|
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|
|
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|
"Computes"_compute.html that produce global quantities are those which
|
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|
do not have the word {atom} in their style name. Only a few
|
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|
"fixes"_fix.html produce global quantities. See the doc pages for
|
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|
individual fixes for info on which ones produce such values.
|
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|
"Variables"_variable.html of style {equal} are the only ones that can
|
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|
be used with this fix. Variables of style {atom} cannot be used,
|
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|
since they produce per-atom values.
|
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|
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|
The {Nevery} argument specifies on what timesteps the input values
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|
will be used in order to be stored. Only timesteps that a multiple
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of {Nevery}, including timestep 0, will contribute values.
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|
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:line
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If a value begins with "c_", a compute ID must follow which has been
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|
previously defined in the input script. If no bracketed term is
|
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|
appended, the global scalar calculated by the compute is used. If a
|
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|
bracketed term is appended, the Ith element of the global vector
|
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|
calculated by the compute is used.
|
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|
|
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|
Note that there is a "compute reduce"_compute_reduce.html command
|
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|
which can sum per-atom quantities into a global scalar or vector which
|
||||||
|
can thus be accessed by fix vector. Or it can be a compute defined
|
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|
not in your input script, but by "thermodynamic
|
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|
output"_thermo_style.html or other fixes such as "fix nvt"_fix_nh.html
|
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|
or "fix temp/rescale"_fix_temp_rescale.html. See the doc pages for
|
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|
these commands which give the IDs of these computes. Users can also
|
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|
write code for their own compute styles and "add them to
|
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|
LAMMPS"_Section_modify.html.
|
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|
|
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|
If a value begins with "f_", a fix ID must follow which has been
|
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|
previously defined in the input script. If no bracketed term is
|
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|
appended, the global scalar calculated by the fix is used. If a
|
||||||
|
bracketed term is appended, the Ith element of the global vector
|
||||||
|
calculated by the fix is used.
|
||||||
|
|
||||||
|
Note that some fixes only produce their values on certain timesteps,
|
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|
which must be compatible with {Nevery}, else an error will result.
|
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|
Users can also write code for their own fix styles and "add them to
|
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|
LAMMPS"_Section_modify.html.
|
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|
|
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|
If a value begins with "v_", a variable name must follow which has
|
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|
been previously defined in the input script. Only equal-style
|
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|
variables can be referenced. See the "variable"_variable.html command
|
||||||
|
for details. Note that variables of style {equal} define a formula
|
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|
which can reference individual atom properties or thermodynamic
|
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|
keywords, or they can invoke other computes, fixes, or variables when
|
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|
they are evaluated, so this is a very general means of specifying
|
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|
quantities to be stored by fix vector.
|
||||||
|
|
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|
:line
|
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|
|
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|
[Restart, fix_modify, output, run start/stop, minimize info:]
|
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|
|
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|
No information about this fix is written to "binary restart
|
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|
files"_restart.html. None of the "fix_modify"_fix_modify.html options
|
||||||
|
are relevant to this fix.
|
||||||
|
|
||||||
|
This fix produces a global vector or global array which can be
|
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|
accessed by various "output commands"_Section_howto.html#howto_15.
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|
The values can only be accessed on timesteps that are multiples of
|
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|
{Nevery}.
|
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|
|
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|
A vector is produced if only a single input value is specified.
|
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|
An array is produced if multiple input values are specified.
|
||||||
|
The length of the vector or the number of rows in the array grows
|
||||||
|
by 1 every {Nevery} timesteps.
|
||||||
|
|
||||||
|
If the fix prouduces a vector, then the entire vector will be either
|
||||||
|
"intensive" or "extensive", depending on whether the values stored in
|
||||||
|
the vector are "intensive" or "extensive". If the fix produces an
|
||||||
|
array, then all elements in the array must be the same, either
|
||||||
|
"intensive" or "extensive". If a compute or fix provides the value
|
||||||
|
stored, then the compute or fix determines whether the value is
|
||||||
|
intensive or extensive; see the doc page for that compute or fix for
|
||||||
|
further info. Values produced by a variable are treated as intensive.
|
||||||
|
|
||||||
|
No parameter of this fix can be used with the {start/stop} keywords of
|
||||||
|
the "run"_run.html command. This fix is not invoked during "energy
|
||||||
|
minimization"_minimize.html.
|
||||||
|
|
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|
[Restrictions:] none
|
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|
|
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|
[Related commands:]
|
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|
|
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|
"compute"_compute.html, "variable"_variable.html
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|
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|
[Default:] none
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||||||
Loading…
Reference in New Issue