10. Learning and extensions

Three lines change what the guard carries inside: learn sets how fast it learns, and add adds attractors and games.

learn: how fast the guard learns

The guard slowly learns how much each criterion weighs in the w_o / w_f split. The learn line limits that learning.

guard learner
  learn: max 0.01

• learn: frozen: criterion weights do not change. This is the default.
• learn: max NUMBER: one learned weight may change by at most NUMBER in one step. The number is above 0 and at most 1.

Why there is an upper limit

A guard that learns can be poisoned. A patient attacker sends messages that each move a weight a little, until the guard starts reading situations differently.

The limit slows that down and makes it visible. With learn: max 0.01, moving one weight by 0.5 takes at least 50 steps. That is enough time to see the shift with the status command.

When to use frozen

• During measurement and comparison, so that two runs give the same result.
• When you suspect someone is poisoning the learning.
• Until you have seen how the guard behaves in observe mode.

add attractor: one more attractor

The four base attractors are always on. When some behavior needs separate analysis, a new one is added:

guard extended
  add attractor learned-helplessness
  add game stag-hunt
  on learned-helplessness: modify
  on dwell(learned-helplessness) -> infinity: escalate human

The name learned-helplessness is illustrative. The add line only turns the attractor on. Its formula must already exist in the PSE library.

An added attractor is used like a base one: as a rule condition and inside dwell(...).

add game: one more game

add game NAME adds a game to the set PSE uses to estimate the counterpart’s behavior. Here too the formula must exist in the library. The name stag-hunt is illustrative.

There is no remove

The language has no command for removal. You cannot turn off a base attractor, and you cannot empty the game set. What you added yourself you remove by deleting the add line from the file.

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Next: 11. Commands: check, explain, status Part of The PSE Language, a textbook by Andrej Ristić. Try the examples in the PSE Playground.