Hi all,
I am solving an ODE with an events function, which requires that it gets stopped after a certain criterion is reached in its response, which can only be determined by employing the previous values of the ODE's solution. To demonstrate that problem I have written this simple code below.
The only way I could think of achieving my above objective was by using persistent variables in the ODE events function. This allows me to keep the previous values of the solution whilst the ODE is being solved, and thus terminate it when the specific criterion is reached.
However I run into the following problem: Every time I run the script, either to debug or for any other purpose, the persistent variables are not cleared. So I have to clear them manually, and the process becomes quite tedious, and prone to error as I forget to clear all the appropriate ones some times. I have looked in to how I can clear those variables in the eventsfcn function, however I do not think that its possible to do that automatically.
Hence my question comes in two parts:
- Can I clear the persistent variables automatically before I run my code every time?
- In case not, is there a better way to achieve my above objective by not utilising persistent variables?
clear ; clc
m = 10 ;
k = 10 ;
f = 10 ;
tol = 1e-3 ;
opts = odeset('Events', @(t, y) eventfcn(t, y, tol)) ;
tspan = [0 10];
y0 = [1 0];
sol = ode15s(@(t, y) odefcn(t, y, m, k, f), tspan, y0, opts);
figure
plot(sol.x, sol.y(2,:))
function [v, i, d] = eventfcn(t, y, tol)
persistent Y n
if isempty(n)
n = 0 ;
Y = 0 ;
end
n = n + 1 ;
Y(n) = y(2) ;
if numel(Y) > 2
err = diff(Y(end-1:end))/Y(end) ;
else
err = nan ;
end
if err <= tol
v = 0 ;
else
v = 1 ;
end
i = 1 ;
d = 0 ;
end
function dydt = odefcn(t, y, m, k, f)
dydt = [y(1) ; -(k*y(2) - f)/m] ;
end
