forked from lijiext/lammps
82 lines
2.6 KiB
Plaintext
82 lines
2.6 KiB
Plaintext
"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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if command :h3
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[Syntax:]
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if value1 operator value2 then command1 else command2 :pre
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value1 = 1st value
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operator = "<" or "<=" or ">" or ">=" or "==" or "!="
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value2 = 2nd value
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then = required word
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command1 = command to execute if condition is met
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else = optional word
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command2 = command to execute if condition is not met (optional argument) :ul
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[Examples:]
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if $\{steps\} > 1000 then exit
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if $x <= $y then "print X is smaller = $x" else "print Y is smaller = $y"
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if $\{eng\} > 0.0 then "timestep 0.005"
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if $\{eng\} > $\{eng_previous\} then "jump file1" else "jump file2" :pre
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[Description:]
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This command provides an in-then-else test capability within an input
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script. Two values are numerically compared to each other and the
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result is TRUE or FALSE. Note that as in the examples above, either
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of the values can be variables, as defined by the
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"variable"_variable.html command, so that when they are evaluated when
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substituted for in the if command, a user-defined computation will be
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performed which can depend on the current state of the simulation.
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If the result of the if test is TRUE, then command1 is executed. This
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can be any valid LAMMPS input script command. If the command is more
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than 1 word, it should be enclosed in double quotes, so that it will
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be treated as a single argument, as in the examples above.
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The if command can contain an optional "else" clause. If it does and
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the result of the if test is FALSE, then command2 is executed.
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Note that by jumping to a label in the same input script, the if
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command can be used to break out of a loop. See the "variable
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delete"_variable.html for info on how to delete the associated loop
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variable, so that it can be re-used later in the input script.
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Note that if either command1 or command2 is a bogus LAMMPS command,
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such as "exit" in the first example, then executing the command will
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cause LAMMPS to halt.
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Here is an example of a double loop which uses the if and
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"jump"_jump.html commands to break out of the inner loop when a
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condition is met, then continues iterating thru the outer loop.
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label loopa
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variable a loop 5
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label loopb
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variable b loop 5
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print "A,B = $a,$b"
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run 10000
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if $b > 2 then "jump in.script break"
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next b
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jump in.script loopb
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label break
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variable b delete :pre
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next a
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jump in.script loopa :pre
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[Restrictions:] none
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[Related commands:]
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"variable"_variable.html
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[Default:] none
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