The tempfile is written regularly during a simulation, depending on the optimization algorithm. It always contains the potential with the currently lowest sum of squares.

The file can be used to plot the current potential to see if it contains some unwanted features.

Every time a new minimum in the sum of squares is discovered, the tempfile is written.

Same as Simulated Annealing, tempfile always contains the potential with the lowest sum of squares.

Once every time the outer loop has successfully completed. This means after every line that is written to standard output the tempfile is written.