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12.4.7 Checkpoint and Restart Options

Since conformational searches can execute for long periods of time, it is necessary to be able to save the state of search and restart it at a later point in time. The CHECKPOINT and RESTART options provide this capability. The frequency of checkpoints are also used to specify the frequency of status writing operations. Finally, a checkpoint is written at the end of the run, so that a long run that is terminated by your options can be continued at greater length later.

The CHECKPOINT options are as follows:

The UNIT options specifies what file unit the checkpoints should be written to. If this is omitted or given a value of -1, then no checkpoints are written. CONGEN handles the file attached to this unit in a special way. When a checkpoint is about to be written, CONGEN attempts to determine the name of the file associated with the unit. It then issues an operating system command to rename or move the file to a different name made up of the original name concatenated with _bak. On VMS systems, any previous _bak file is deleted first. Then, a new file with the original name is opened, and the checkpoint is written. Thus, one good checkpoint file is always maintained, and usually there are two.

The NODEFREQ option specifies how many nodes must be allocated between writing a checkpoint. The default is 100000.

The TIMEFREQ option specifies the time in minutes between writing checkpoint files. Checkpoints are written when either NODEFREQ or TIMEFREQ tests are passed, and both the counters and timers are reset when the checkpoint is written.

This options controls when CONGEN periodically flushes the output buffers for the log file (Fortran unit 6) and the output files specified in the write coordinate degrees of freedom. This option is normally on, but it can be turned off using NOFLUSH.

To restart a CONGEN run, one should edit the CONGEN input file that used for the checkpoint file, and a RESTART option should be used. The unit number specified in the RESTART option should be a valid checkpoint from a previous run. It is permitted to change the options which control the operation of search such as MAXNODE and MAXLEAF, but the degrees of freedom must not be changed. Only limited testing of option changing has been performed after restarting, so be careful.