Solving very stiff system of ODE's

Hi

I have the following system of ODEs (a very stiff system!):

eoms = @(t,x) [
    3.9e3 + 4.8e4*x(3) - 3.9e3*0.02*x(1);
    3.9e3*0.2*x(1) - x(2)*3.3e3;
    2.2e3*x(2) - 4.8e4*x(3) + heaviside(t-1)*x(5)*2.8e7;
    1.1e3*x(2) - heaviside(t-1)*4.7e7*x(4);
    heaviside(t-1)*(4.7e4*x(4) - 2.8e7*x(5)-9.0e6*x(5))];

x0 = [0 0 0 0 0];
tspan = [0 1];
[t, x] = ode23s(eoms, tspan, x0);

figure(1)
plot(t, x(:, 1))

When I run the script, I get the message: "Failure at t=1.000000e+000. Unable to meet integration tolerances without reducing the step size below the smallest value allowed (3.552714e-015) at time t."

I'm not quite sure if I can do anything about it, but I thought that I should ask in here first. The timestep can't get any lower -- and I am already using a solver suitable for stiff systems. Do I have any options left?

Best, Niles.

Answer 1

[Sean de Wolski]

Give it a better x0