Ode23 is not outputting solutions at the times I specified between t0 and tf in tspan=[t0, t1, t2..., tf]
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Spencer
am 14 Sep. 2024 um 20:17
Kommentiert: Spencer
am 14 Sep. 2024 um 20:30
I am using ode23() to solve an ODE between t=0 and t=7, and I want solutions at every 0.1 seconds. I am calling ode23 with tspan=[0, 0.1, 0.2, ..., 7] (which is 71 entries long) but the output solution is only 38 entries long at the times chosen by the solver. It is exactly the same as when tspan=[0 7]. Why is not listening to the argument I gave?
% define ODE
function dydt = myfun(t, y, c, m, g)
v = sqrt(y(2)^2+y(4)^2);
dydt = [y(2); -c*v*y(2)/m; y(4); -c*v*y(4)/m-g];
end
% Simulate ODE
c = 0.028;
m = 0.3;
g = 9.81;
y0 = [0; 35*cosd(65); 0; 35*sind(65)];
times = [0:0.1:7];
soln = ode23(@(t, y) myfun(t, y, c, m, g), times, y0);
xc = soln.y(1, :)';
yc = soln.y(3, :)';
figure
plot(xc, yc)
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Torsten
am 14 Sep. 2024 um 20:23
Bearbeitet: Torsten
am 14 Sep. 2024 um 20:28
If you use the "soln" structure as result, ode23 only respects start and end point from your tspan vector.
After the integrator has finished, you would have to use "deval" to interpolate the solution to the time points of your choice.
I suggest using the [T,Y] solution structure instead:
% Simulate ODE
c = 0.028;
m = 0.3;
g = 9.81;
y0 = [0; 35*cosd(65); 0; 35*sind(65)];
times = [0:0.1:7];
[T,Y] = ode23(@(t, y) myfun(t, y, c, m, g), times, y0);
xc = Y(:,1);
yc = Y(:,3);
figure
plot(xc, yc)
% define ODE
function dydt = myfun(t, y, c, m, g)
v = sqrt(y(2)^2+y(4)^2);
dydt = [y(2); -c*v*y(2)/m; y(4); -c*v*y(4)/m-g];
end
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