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docs:utils:options [2010/02/02 07:55] (current)
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 +====== Utility options ======
 +
 +The channelflow utilities are stand-alone command-line programs that are run 
 +from the Unix shell. You can get brief built-in help information on each
 +utility by running it with a -h or --help option. For example, running
 +"​couette --help"​ produces
 +
 +  gibson@akbar$ couette --help
 +  couette :
 +        integrate an initial condition and save velocity fields to disk.
 +
 +  options :
 +    -T0       ​--T0 ​          <​real> ​  ​default == 0       start time
 +    -T1       ​--T1 ​          <​real> ​  ​default == 100     end time
 +    -vdt      --variabledt ​                              ​adjust dt for CFL
 +    -dt       ​--dt ​          <​real> ​  ​default == 0.03125 timestep
 +    -dtmin ​   --dtmin ​       <​real> ​  ​default == 0.001   ​minimum time step
 +    -dtmax ​   --dtmax ​       <​real> ​  ​default == 0.05    maximum time step
 +    -dT       ​--dT ​          <​real> ​  ​default == 1       save interval
 +    -CFLmin ​  ​--CFLmin ​      <​real> ​  ​default == 0.4     ​minimum CFL number
 +    -CFLmax ​  ​--CFLmax ​      <​real> ​  ​default == 0.6     ​maximum CFL number
 +    -ts       ​--timestepping <​string>​ default == sbdf3   ​timestepping algorithm
 +    ...
 +     ​-p ​       --pressure ​                               print pressure grad
 +    <​flowfield> ​     (trailing arg 1)                    initial condition
 +
 +The built-in help gives a brief description of each utility'​s purpose
 +
 +and a list of its command-line options and arguments. Channelflow
 +utilities are invoked at the command line with syntax like
 +
 +   ​utility -opt1 value -opt2 value -flag1 arg3 arg2 arg1
 +
 +or concretely
 +
 +   ​couette -T0 0 -T1 -vdt -dt 0.02 -ts sbdf4 u0.ff
 +
 +
 +"​Options"​ (e.g. ''​-opt1 value''​) are used to reset default values
 +of parameters. For options, the first two columns in the built-in
 +help give the short and long form of the option (e.g. ''​-ts''​ and
 +''​--timestepping''​),​ the third column indicates the type of parameter
 +expected (e.g. ''​real,​ int, bool, string''​),​ and the fourth gives the
 +the default value. For example, ''​couette -dt 0.02 -ts cnab2''​ sets
 +the time stepping method to 2nd order Crank-Nicolson Adams-Bashforth
 +with dt=0.02.
 +
 +"​Flags"​ simply turn on boolean options that would otherwise be set
 +to false. For example, calling ''​couette -vdt''​ turns on variable-dt
 +timestepping,​ which adjusts dt at fixed intervals to keep the CFL
 +number within bounds. For flags the third and fourth columns of
 +built-in help are left blank.
 +
 +"​Arguments"​ always come after all options and flags. Arguments usually
 +specify the filenames of binary velocity fields that the utility will
 +load and operate on. Most channelflow programs have one required
 +argument (e.g. ''​couette u0.ff''​) some two (e.g. ''​L2Dist u0.ff u2.ff''​).
 +Others take a variable number of arguments (e.g. ''​makebasis u0 u1 u''​).
 +Unfortunately it's difficult to document variable-number arguments
 +properly in the four-column option system, so variable-number arguments
 +are usually documented with a "​usage:"​ line right after the description
 +of the utility'​s purpose.
 +
 +So, as you read work through the Example Calculations,​ you can run the
 +suggested command with a ''​-h''​ or ''​--help''​ option to clarify what the 
 +options are doing and what other options are possible.
 +
  
docs/utils/options.txt ยท Last modified: 2010/02/02 07:55 (external edit)