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Error in using ode45 for solution of nonlinear system of three equations which are interlinked to each other

3 vues (au cours des 30 derniers jours)
% Define the ODE system
f = @(t,x) [-(p1 + x(2)) * x(1) + p1 * Gb + D; -p2 * x(2) + p3 .* x(3) + p3.* Ib; -n * (x(3) - Ib) + u];
% Solve the ODE system
[t,x] = ode45(f, tspan, [x1; x2; x3]);
Error using vertcat
Dimensions of arrays being concatenated are not consistent.
Error in UpdatedTrialsmc>@(t,x)[-(p1+x(2))*x(1)+p1*Gb+D;-p2*x(2)+p3.*x(3)+p3.*Ib;-n*(x(3)-Ib)+u] (line 51)
f = @(t,x) [-(p1 + x(2)) * x(1) + p1 * Gb + D; -p2 * x(2) + p3 .* x(3) + p3.* Ib; -n * (x(3) - Ib) + u];
Error in UpdatedTrialsmc (line 54)
[t,x] = ode45(f, tspan, [x1; x2; x3]);

Réponses (3)

Torsten
Torsten le 12 Avr 2023
Déplacé(e) : Torsten le 12 Avr 2023
Check
size(p1)
size(Gb)
size(D)
size(p2)
size(p3)
size(Ib)
size(n)
size(u)
If one of the sizes is not 1x1 (a scalar), your code won't work.
  2 commentaires
FAIZ UL HASSAN
FAIZ UL HASSAN le 12 Avr 2023
All are scalar, have single constant value which is defined earlier in the code.
Torsten
Torsten le 12 Avr 2023
All are scalar, have single constant value which is defined earlier in the code.
If you get the error message as stated, this can't be true.

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Bjorn Gustavsson
Bjorn Gustavsson le 12 Avr 2023
Perhaps you need to check the size of each component in your ode-function:
f = @(t,x) [-(p1 + x(2)) * x(1) + p1 * Gb + D; -p2 * x(2) + p3 .* x(3) + p3.* Ib; -n * (x(3) - Ib) + u];
What are the sizes of p1, Gb, D, p2, p3, Ib, n, Ib and u? The error-message you get is what I typically get when I try to concatenate arrays of incompatible sizes.
HTH

Sam Chak
Sam Chak le 12 Avr 2023
Modifié(e) : Sam Chak le 12 Avr 2023
Try this:
% Define the time-varying Disturbance
D = @(t) sin(pi/10*t);
% Define the scalar parameters
Gb = 1;
n = 1;
p1 = 1;
p2 = 1;
p3 = 1;
Ib = 1;
% Define the feedback input u
u = @(x) - x(1) - 2*x(2);
% Define the system dynamics
f = @(t, x) [-(p1 + x(2))*x(1) + p1*Gb + D(t);
- p2*x(2) + p3*x(3) + p3*Ib;
- n*(x(3) - Ib) + u(x)];
% Define the initial conditions
x0 = [1; 0; 0];
% Define the time interval
tspan = [0 20];
% Solve the system using the ode45 solver
[t, x] = ode45(f, tspan, x0);
% Plot the result
plot(t, x); grid on
xlabel('t')
  4 commentaires
Sam Chak
Sam Chak le 12 Avr 2023
Modifié(e) : Sam Chak le 12 Avr 2023
Thanks @FAIZ UL HASSAN. It looks a little complicated to read the equation this way without breaking up the terms. But some parameters are unavailable. Try simplifying u by making up u1, u2, u3, ... This helps troubleshooting later. I guess that the error "Dimensions of arrays being concatenated are not consistent" is caused by u.
Edit: On a second look, I'm just guessing...💡 that u is some kind of a sliding mode forcing input structure and e, ed, edd refers to , respectively. S must be the sliding surface then.
Besides, check if sign(S) is a discontinuous function or just a scalar like this
sign(3.14159)
ans = 1
The ode45() solver does not work well with discontinuous function when .

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