States node

[jonathanjfshaw]

A state machine is a fundmental programming pattern, and keeping track of states is a natural part of many biofeedback and BCI apps. Therefore I suggest having a state machine node in core.

Proof that this should be core comes from the fact that the state machine implementation I have developed would make it possible to deprecate the Periodic and Gate nodes.

[jonathanjfshaw]

Here's how you would get a gate by combining a States node and an ExpressionFilter from #65:

nodes: 
    - id: my_data_source 
      ...
    - id: my_event_source
      ... 
    - id: my_gate
      module: timeflux.nodes.states
      class: States
      params:
        states: ['close', 'open']
    - id: my_filter
      module: timeflux.nodes.expression
      class: ExpressionFilter
      params:
        expression: i_gate == 'open'
        eval_on: ports

    edges:
    - source: my_data_source
      target: my_gate
    - source: my_event_source
      target: my_gate:events
    - source: my_data_source
      target: my_filter
    - source: my_gate
      target: my_filter:gate

[jonathanjfshaw]

Here's how you would get a periodic event by combining 2 states.

This example will send 5 events called "on" (spaced 200ms apart) whenever it is triggered, except not in the first 30 seconds of its life. There's no requirement for a manual trigger, I could just as well have made it be triggered automatically every 10 seconds.

nodes: 
   - id: trigger
    ...
    - id: phase
      module: timeflux.nodes.states
      class: States
      params:
        states: ['wait','quiet', 'active']
        properties: 
          wait: # This is the initial state, preventing anything from happenig in first 30 seconds.
            min_seconds: 30
            auto_transition: quiet
            auto_transition_seconds: 30
          active: # Bursts of activity last for exactly 1 second when the event "active" is received
            min_seconds: 1
            auto_transition: quiet
            auto_transition_seconds: 1
    - id: flicker # Flickers happen constantly every 200ms
      module: timeflux.nodes.states
      class: States
      params:
        states: ['on']
        properties: 
          on:
            auto_transition: on
            auto_transition_seconds: 0.2
    - id: flashes # We want the flickers to pass through only in the "active" phase
      module: timeflux.nodes.expression
      class: ExpressionFilter
      params:
        expression: i_flicker == 'on' and i_phase == 'active'
        eval_on: ports
    - id: flashes_only # If we don't want NaNs in the quiet phase, we can remove them
      module: timeflux.nodes.missing
      class: Missing
      params:
        dropna: True

    edges:
    - source: trigger
      target: phase:events
    - source: phase:transitions
      target: flashes:phase
    - source: flicker:transitions
      target: flashes:flicker
    - source: flicker:transitions
      target: flashes
    - source: flashes
      target: flashes_only