# Restart¶

MICRESS® allows the user either to start a new simulation (new) or to restart from the last output of an old one (restart). The restart option thus gives the possibility to continue a stopped simulation or to start various simulations (e.g. for a parameter variation) from a common starting point defined by a previous simulation. Thus, calculation time and effort can be saved.

Example Restart

...
# Restart
# ===============
# Restart using old results?
# Options:    new       restart [reset_time | with_flow]
restart
# Name of restart file?
aRestartFile
...


Note: Even if the restart option is used, all input parameters have to be specified like for a new simulation run. Those parameters which represent initial conditions like initial composition and temperature are replaced automatically by the values from the restart file.

Important: Extreme caution should be exercised when modifying parameters in conjunction with the restart feature. Several parameters like the size of the simulation domain (in cells), the number of used elements and phases, the number of diffusion contributions or nucleation types cannot be changed due to compatibility reasons. Which parameters can be changed depends also on the optional keyword which is used in the same line with restart (see example for available options). Furthermore, the restart file must have been created using a MICRESS® version higher than 6.4 and the same computer type.

If the restart option is used, the path and name of the restart file (without extension) has to be given in the next line. The restart file can be taken from a previous simulation. It has the extension .rest and is automatically created for the latest output time step if the corresponding restart output option is specified (see below).

The optional keyword reset_time in the same line after restart allows resetting the simulation time to $0$. This is convenient for simulation of multiple process steps because e.g. the temperature-time history needs not to be repeated through all driving files for the different process steps and the initial temperature can be explicitly given in case of restart. Furthermore, all internal timers (e.g. for relinearisation or nucleation checks in certain intervals or internal diffusion time stepping) are reinitialized. This has the positive side effect that the number of diffusion contributions or nucleation types can now be modified!

The with_flow option should be used when fluid flow should be enabled during the restart, i.e. the restart file was created from a simulation without flow. For this simulation the fluid flow module should be switched on as described in the flow solver topic. It is recommended to either keep a copy of the old restart file or change the output location to avoid overwriting the restart file chosen as starting point for fluid simulations when configuring numerical parameters for fluid flow.