GfsTime

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Revision as of 05:39, 23 April 2008
GeordieMcBain (Talk | contribs)
(linked to rt.html for example of dtmax)
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GeordieMcBain (Talk | contribs)
(noted that i>0 suppresses the divergence-free projection of initial velocity)
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-'''GfsTime''' defines the physical and the computational time. By “computational time” I mean the number of time steps performed. By default both the physical time and the time step number are zero when the program starts. It is possible to set different values using for example+'''GfsTime''' defines the starting and finishing time for the run, either in terms of the floating-point model time or the integer time-step number, or a combination. By default both floating-point ''t'' and time-step number ''i'' are zero when the program starts, but it is possible to set different values using for example
GfsTime { t = 1.4 i = 32 end = 0 } GfsTime { t = 1.4 i = 32 end = 0 }
-where i is the time step number and t is the physical time. The end identifier specifies that the simulation should stop when the physical time reaches the given value. It is also possible to stop the simulation when a specified number of time steps is reached, using the iend identifier. If both end and iend are specified, the simulation stops when either of these are reached. By default, both end and iend values are infinite.+and it will be found that this is done in the files produced by [[GfsOutputSimulation]] so that these can be used to restart runs. (''Technical note:'' if ''i'' is zero, as it is by default but not in a restart, the initial velocity field is projected onto the divergence-free subspace before the simulation begins.)
-Another parameter, dtmax, can be used to cap the time-step, as in the [http://gfs.sourceforge.net/examples/examples/rt.html#htoc5 Rayleigh–Taylor] example+The ''end'' and ''iend'' identifiers specify that the simulation should stop when the floating-point model time reaches the given value or the prescribed number of steps have been taken, whichever comes first; either stopping criterion is ignored if its keyword is omitted.
 + 
 +Another parameter, ''dtmax'', can be used to cap the time-step, as in the [http://gfs.sourceforge.net/examples/examples/rt.html#htoc5 Rayleigh–Taylor] example
Time { end = 1 dtmax = 5e-3 } Time { end = 1 dtmax = 5e-3 }

Current revision

GfsTime defines the starting and finishing time for the run, either in terms of the floating-point model time or the integer time-step number, or a combination. By default both floating-point t and time-step number i are zero when the program starts, but it is possible to set different values using for example

 GfsTime { t = 1.4 i = 32 end = 0 }

and it will be found that this is done in the files produced by GfsOutputSimulation so that these can be used to restart runs. (Technical note: if i is zero, as it is by default but not in a restart, the initial velocity field is projected onto the divergence-free subspace before the simulation begins.)

The end and iend identifiers specify that the simulation should stop when the floating-point model time reaches the given value or the prescribed number of steps have been taken, whichever comes first; either stopping criterion is ignored if its keyword is omitted.

Another parameter, dtmax, can be used to cap the time-step, as in the Rayleigh–Taylor example

 Time { end = 1 dtmax = 5e-3 }
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