I think you have a misconception that can be quickly cleared up. Take a look at the documentation of custom plot functions.
The misconception is that MATLAB fills in options, state, and flag. You are free to read and use those values, but you do not have to.
The syntax is, in fact,
function state = plotfun(options,state,flag)
If you want the plot function to stop the solver, follow this prescription: set state.StopFlag to a nonempty string.
Good luck,
Alan Weiss
MATLAB mathematical toolbox documentation
