ode45

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Villanova
Villanova on 10 Dec 2011
I am trying to use ODE45. I am just wondering why my plots are just constant lines. Is it possible if anyone could kindly help me out. Those parameters that I have are purely made up, since there is no way to come up with them at this moment because I am not doing System Identification. I did my best to guess them correctly, but I didn't have much luck. Thanks. The first code is:
function xdot=bond_boat(t,x)
global vr L R T G vl B tp vw Ry m mu Q vwdot Rx K Rtheta Jp J
xdot(1,1)=(vr/L)-(R/L)*x(1)-((T*G)/(2*L))*(x(4)+x(5));
xdot(2,1)= (vl/L)-(R/L)*x(2)-((T*G)/(2*L))*(x(4)-x(5));
xdot(3,1)= -1/(2*B)*(tp^2*x(5)*x(4)+ 2*tp*vw*x(5)) - Ry/m;
xdot(4,1) = ((T*G)/Q)*x(4) -((mu*tp)/Q)*(m*vwdot - (m*tp/B)*x(3)*x(5) - Rx);
xdot(5,1) = ((T*G)/K)*x(5)- ((mu*tp)/(B*K))*(m*x(3)*(tp*x(4) + 2*vw) + 2*Rtheta);
and the second code is as the following clc close all clear all
global vr L R T G vl B tp vw Ry m mu Q vwdot Rx K Rtheta Jp J
vr = .03;
L= 10;
G = 6;
vl = .03;
B = 0.1;
T = (B/2)*(.001);
tp = 10;
vw = .01 ;
Ry = .2 ;
m = 1.34;
mu = .1;
vwdot = 0 ;
Rx = .2;
Rtheta= .2 ;
Jp = .1;
Q = Jp + .5*mu*(tp^2)*m;
J = .03;
K = Jp + (2*mu*(tp^2)* J/(B^2));
R = 2;
ic=[0.1;10;.01;1;0] ;
time = [0 10];
[t,x] = ode45('bond_boat', time, ic);
subplot(5,1,1);
plot(t,x(1),'red')
xlabel('Time');
ylabel('X_1');
subplot(5,1,2);
plot(t,x(2),'blue')
xlabel('Time');
ylabel('X_2');
subplot(5,1,3);
plot(t,x(3),'red')
xlabel('Time');
ylabel('X_3');
subplot(5,1,4);
plot(t,x(2),'blue')
xlabel('Time');
ylabel('X_{4new}');
subplot(5,1,5);
plot(t,x(5),'red')
xlabel('Time');
ylabel('X_{5new}');

Accepted Answer

Mohsen  Davarynejad
Mohsen Davarynejad on 10 Dec 2011
The only thing you have to do is to change
plot(t,x(1),'red')
to
plot(t,x(:,1),'red')
and so on for the rest of plots. The rest of the code is not optimial, but its ok. To do a better job, you could pass the global variables to the ode45 as an input argument.
  2 Comments
Mohsen  Davarynejad
Mohsen Davarynejad on 11 Dec 2011
Salam Farshad, Khahesh mikonam. Na rastesh, man Control kar boodam :), valy alan bishtar Computer science hastam.

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