Is it possible to use an anonymous function as an event-function when solving an ODE in Matlab

Question

Is it possible to use an anonymous function as an event function in Matlab. What I want to do is basically

opt = odeset('Events', @(t,y) (deal(y(end)-t^2,1,0)));
[T,Y] = ode45(@odefun,[tstart tend],y0,opt);

However, this returns an error complaining that the number of outputs to deal must be matched exactly. Is there some other way to make the anonymous function return multiple arguments?

Answer 1

Also (this is very late in the game to be adding to this, but this frustrates me). Here is a solution with nested functions:

function [ dealfunchandle ] = dealwithit( arrayfunc )
% Takes as input an event function of (t,z) that returns a 3 array (in same order as event syntax).

    function [a, b, c] = dealfunc(t,z)
       output = arrayfunc(t,z);
       a = output(:,1);
       b = output(:,2);
       c = output(:,3);
    end

dealfunchandle = @dealfunc;
end

This function only has to be written once (handy if you have to use lots of different event functions). This can be used to generate an anonymous event function within the code as follows:

arrayfunc = @(t,y) [y(1), 0, 1];
events = dealwithit(arrayfunc);

opts = odeset('Events', events);

And then ode45 as per normal.

Answer 2

I noticed this post looking for the answer to the same question. This means that for some people the question may be still valid. Since finally I found the solution by myself, I'd like to give a little bit "outdated" answer.

Actually, yes - it's possible but not straightforward. Try this:

evnt_fun = @(t, f)subsref({'some stop condition', 1, 0}, struct('type', '{}', 'subs', {{':'}}));

I'm not able to fully check the backward-compatibility of the code. However, it works with R2011 and later MATLAB versions.

Answer 3

No, you can't do it. Anonymous functions in Matlab only ever return one value.

Instead, you could define a thin wrapper around deal and pass your wrapper as a handle:

function [a b c] = wrapper(t,y)
    [a b c] = deal('some stop condition', 1, 0);
end

opt = odeset('Events', @wrapper);

[T, Y] = ode45(@odefun, [tstart tend], y0, opt);