How to solve ODE for varying input using ode23 ?
2 views (last 30 days)
Show older comments
I'm trying to solve a RC circuit using ode23. For my case the input is varying with time. Here u is my input vector.
% function
function vdot = diff3(t,v)
u = [1 2 3 4 5] ;
vdot(1) = -40*v(1) + 20*v(2) + 20*u(t);
vdot(2) = 20*v(1) - 20*v(2) - v(3);
vdot(3) = 0.1*v(2) -1000*v(3);
vdot = [vdot(1);vdot(2);vdot(3)];
end
% main program
tspan = 1:5;
x0 = [0 0 0]; % initial conditions
[t,x] = ode23('diff3', tspan, x0);
tt = length(t);
for i = 1:tt
vo(i) = x(i,1) - x(i,2);
end
plot(t, vo)
title('Transient analysis of RLC')
xlabel('Time, s'), ylabel('Output voltage')
In case of fixed value of u = 5, there is no error. As my input is varying MATLAB is throwing some error. _
Attempted to access u(1); index must be a positive integer or logical.
Error in diff3 (line 9)
vdot(1) = -40*v(1) + 20*v(2) + 20*u(t);
Error in ode23 (line 256)
f(:,2) = feval(odeFcn,t+h*A(1),y+f*hB(:,1),odeArgs{:});
Error in rcckt (line 5)
[t,x] = ode23('diff3', tspan, x0);_
So how can I solve ODE for varying input? Any kind of suggestion will be really helpful. Thanks in advance!
0 Comments
Accepted Answer
Torsten
on 25 Aug 2016
% function
function vdot = diff3(t,v)
u = [1 2 3 4 5] ;
tu = [1 2 3 4 5];
u_at_t = interp1(tu,u,t);
vdot(1) = -40*v(1) + 20*v(2) + 20*u_at_t;
vdot(2) = 20*v(1) - 20*v(2) - v(3);
vdot(3) = 0.1*v(2) -1000*v(3);
vdot = [vdot(1);vdot(2);vdot(3)];
end
Best wishes
Torsten.
2 Comments
Torsten
on 26 Aug 2016
Since interp1 only returns a scalar in each case,
function vdot = diff3(t,v)
u = [1 2 3 4 5;
6 7 8 9 10;
11 12 13 14 15] ;
tu = [1 2 3 4 5];
u_at_t(1) = interp1(tu,u(1,:),t);
u_at_t(2) = interp1(tu,u(2,:),t);
u_at_t(3) = interp1(tu,u(3,:),t);
vdot(1) = -40*v(1) + 20*v(2) + 20*u_at_t(1);
vdot(2) = 20*v(1) - 20*v(2) - v(3) + u_at_t(2);
vdot(3) = 0.1*v(2) -1000*v(3) + u_at_t(3);
vdot = [vdot(1);vdot(2);vdot(3)];
end
also works.
Best wishes
Torsten.
More Answers (0)
See Also
Categories
Find more on Ordinary Differential Equations in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!