different PDEs to solve through events in pdepe

There is a model defined by a pointwise PDE solving for u(x,t), i.e. it is PDE1 when u(x,t)>0 and PDE2 when u(x,t)<=0. Can one use pdepe events to solve this pointwise PDE? I don't think the following code works because once umesh=0 anywhere the whole PDE will be switched to the other (e.g. PDE2 on the global domain rather than locally will be triggered if PDE1 is terminated by events).

function [value, isterminal, direction] = pdevents(m,t,xmesh,umesh)
value = umesh;
isterminal = ones(size(umesh));
direction = zeros(size(umesh));

[Torsten]

Is this switch of the PDE just a thought experiment of yours or do you have a special existing PDE in mind ?

What should happen if u(x,t) > 0 for some x and u(x,t) <= 0 for the other x ? It seems almost impossible to solve two different PDEs depending on the sign of the solution.

[feynman feynman]

Not really a thought experiment. There's plenty of PDEs like that for example if it has a term that is a step function.

[Torsten]

Then you should try to manage these discontinuities within the function that defines the PDE equation, not by using the "events" facility.

"Events" might be useful in this context to stop an integration (e.g. if the PDE has reached a steady state or if some value has reached a certain limit level).

[feynman feynman]

that makes sense, thank you!