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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@4086 f3b2605a-c512-4ea7-a41b-209d697bcdaa

This commit is contained in:
sjplimp 2010-05-05 20:19:26 +00:00
parent 11b28d8711
commit d244f2c40b
2 changed files with 24 additions and 14 deletions

19
doc/variable.html
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@ -519,9 +519,9 @@ after or in between runs, e.g. by including them in a
<A HREF = "print.html">print</A> command. In this case, if a compute is needed to <A HREF = "print.html">print</A> command. In this case, if a compute is needed to
evaluate a variable (either directly or indirectly), LAMMPS will not evaluate a variable (either directly or indirectly), LAMMPS will not
invoke the compute, but it will use a value previously calculated by invoke the compute, but it will use a value previously calculated by
the compute if it is current. Fixes will always provide a quantity the compute, and can do this only if it is current. Fixes will always
needed by a variable, but the quantity may or may not be current. provide a quantity needed by a variable, but the quantity may or may
This leads to one of three kinds of behavior: not be current. This leads to one of three kinds of behavior:
</P> </P>
<P>(1) The variable may be evaluated accurately. If it contains <P>(1) The variable may be evaluated accurately. If it contains
references to a compute or fix, and these values were calculated on references to a compute or fix, and these values were calculated on
@ -530,9 +530,11 @@ used by the variable and the result will be accurate.
</P> </P>
<P>(2) LAMMPS may not be able to evaluate the variable and generate an <P>(2) LAMMPS may not be able to evaluate the variable and generate an
error. For example, if the variable requires a quantity from a error. For example, if the variable requires a quantity from a
<A HREF = "compute.html">compute</A> that is not current, LAMMPS will not do it. <A HREF = "compute.html">compute</A> that is not current, LAMMPS will generate an
This means, for example, that such a variable cannot be evaluated error. This means, for example, that such a variable cannot be
before the first run has occurred. evaluated before the first run has occurred. Likewise, in between
runs, such a variable cannot be accessed unless it was evaluated on
the last timestep of the preceding run, e.g. by thermodynamic output.
</P> </P>
<P>One way to get around this problem is to perform a 0-timestep run <P>One way to get around this problem is to perform a 0-timestep run
before using the variable. For example, these commands before using the variable. For example, these commands
@ -560,7 +562,10 @@ does not change the input state for the 1000-timestep run that
follows. Also note that the 0-timestep run must actually use and follows. Also note that the 0-timestep run must actually use and
invoke the compute in question (e.g. via <A HREF = "thermo_style.html">thermo</A> or invoke the compute in question (e.g. via <A HREF = "thermo_style.html">thermo</A> or
<A HREF = "dump.html">dump</A> output) in order for it to enable the compute to be <A HREF = "dump.html">dump</A> output) in order for it to enable the compute to be
used in a variable after the run. used in a variable after the run. Thus if you are trying to print a
variable that uses a compute you have defined, you could insure it was
invoked on the last timestep of the preceding run by including it in
thermodynamic output.
</P> </P>
<P>Unlike computes, <A HREF = "fix.html">fixes</A> will never generate an error if <P>Unlike computes, <A HREF = "fix.html">fixes</A> will never generate an error if
their values are accessed by a variable in between runs. They always their values are accessed by a variable in between runs. They always

19
doc/variable.txt
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@ -508,9 +508,9 @@ after or in between runs, e.g. by including them in a
"print"_print.html command. In this case, if a compute is needed to "print"_print.html command. In this case, if a compute is needed to
evaluate a variable (either directly or indirectly), LAMMPS will not evaluate a variable (either directly or indirectly), LAMMPS will not
invoke the compute, but it will use a value previously calculated by invoke the compute, but it will use a value previously calculated by
the compute if it is current. Fixes will always provide a quantity the compute, and can do this only if it is current. Fixes will always
needed by a variable, but the quantity may or may not be current. provide a quantity needed by a variable, but the quantity may or may
This leads to one of three kinds of behavior: not be current. This leads to one of three kinds of behavior:
(1) The variable may be evaluated accurately. If it contains (1) The variable may be evaluated accurately. If it contains
references to a compute or fix, and these values were calculated on references to a compute or fix, and these values were calculated on
@ -519,9 +519,11 @@ used by the variable and the result will be accurate.
(2) LAMMPS may not be able to evaluate the variable and generate an (2) LAMMPS may not be able to evaluate the variable and generate an
error. For example, if the variable requires a quantity from a error. For example, if the variable requires a quantity from a
"compute"_compute.html that is not current, LAMMPS will not do it. "compute"_compute.html that is not current, LAMMPS will generate an
This means, for example, that such a variable cannot be evaluated error. This means, for example, that such a variable cannot be
before the first run has occurred. evaluated before the first run has occurred. Likewise, in between
runs, such a variable cannot be accessed unless it was evaluated on
the last timestep of the preceding run, e.g. by thermodynamic output.
One way to get around this problem is to perform a 0-timestep run One way to get around this problem is to perform a 0-timestep run
before using the variable. For example, these commands before using the variable. For example, these commands
@ -549,7 +551,10 @@ does not change the input state for the 1000-timestep run that
follows. Also note that the 0-timestep run must actually use and follows. Also note that the 0-timestep run must actually use and
invoke the compute in question (e.g. via "thermo"_thermo_style.html or invoke the compute in question (e.g. via "thermo"_thermo_style.html or
"dump"_dump.html output) in order for it to enable the compute to be "dump"_dump.html output) in order for it to enable the compute to be
used in a variable after the run. used in a variable after the run. Thus if you are trying to print a
variable that uses a compute you have defined, you could insure it was
invoked on the last timestep of the preceding run by including it in
thermodynamic output.
Unlike computes, "fixes"_fix.html will never generate an error if Unlike computes, "fixes"_fix.html will never generate an error if
their values are accessed by a variable in between runs. They always their values are accessed by a variable in between runs. They always