The simulation buttons

Simulating a machine works differently, depending on whether you have drawn an automaton (deterministic, nondeterministic, or deterministic push-down) or a Turing machine.

On automata

For an automaton, the toolbar contains a single Play button, represented by a green triangle in the toolbar. When you click the Play button, the automaton resets its current state to the initial state, displayed in green. As you type letters, the highlighted states will update to reflect the state transitions of the automaton, and the tape at the window's bottom will log the letters you type. (With the deterministic pushdown automaton, the tape will reflect the contents of the stack instead.)

If you want to simulate a different string entirely, click the Play button again. The tape will clear, and the automaton will reset to its initial state.

The backspace key will work as an ``undo:'' it restores the machine to its state before the last character typed. You can go back several steps.

On Turing machines

Simulating a Turing machine is slightly more complex. Before you use any of the simulation buttons, first type the entire string you want it to read onto the tape. The five simulation buttons work as follows.

• The Play button (pictured as a green triangle) will put the Turing machine into autopilot, stepping through repeatedly until it has gone off the state machine.

• The Pause button (pictured as two vertical red bars) will halt the Turing machine simulation.

• The Step button (pictured as a rightward green triangle adjoining a vertical red bar) will step the Turing machine forward one step only.

• The Rewind button (pictured as a leftward green triangle adjoining a vertical red bar) will undo the most recent step performed by the Turing machine.

• The Reset button (pictured as a red circular arrow) will reset the tape and the machine's state.