Matlab ODEs: unable to meet integration tolerances ( using different types of commands for odes)
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My ODEs system is:
function dydt = SIR1ode(t,y)
[params,zeta,mu,IC]=example(2);
c1 = params(1); c2= params(2);c3= params(3); c4= params(4);
S1 = y(1); S2 = y(2); S3= y(3);
dS1 = -c1*S1-c2*S2^2+2*c3*S2;
dS2 = c2*S1^2 - (c3+c4)*S2;
dS3 = c4*S2;
dydt = [dS1;dS2;dS3];
I call this function from my main script:
tspan = [0,0.2];
% % deterministic model:
[T,Y] = ode23s(@SIR1ode,tspan,[400 798 0]);
Matlab output is:
Warning: Failure at t=3.818112e-04. Unable to meet integration tolerances without
reducing the step size below the smallest value allowed (1.356466e-18) at time t.
> In ode23s at 402
When I tried to plot the solution I find that the initial condition is not taken into account and all the curves start from 0 which is not in harmony with my initial condition [400 798 0].
How can solve this issue? I tried different commands of odes like ODE15S and ode45... but still have the same problem.
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Answers (1)
Torsten
on 24 Jul 2015
If your solution curves all started from 0, MATLAB would not have problems integrating your system because all solution variables remained at 0 for all times (look at your derivatives).
So this cannot be true.
My guess is that your solution blows up such that MATLAB cannot integrate beyond 3.8e-4 s.
Best wishes
Torsten.
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