This will typically be used in a couple of different situations. One is if a number of new subjects have been simulated and their ETAs should be reused in subsequent simulations. Another is internally by NMsim when simulating new subjects from models estimated with SAEM.
genPhiFile(data, file)
Invisibly, character lines (strings) optionally written to file
A dataset that contains "ID" and all ETAs. This can be obtained by `NMdata::NMscanData`.
Path to the .phi file to be written.