Solve 7 DOF Error in MATLAB with Ode45 - Help from Experts

In summary, the conversation is about an individual writing a program to find 7 degrees of freedom, but they keep receiving an error message stating that the argument 'x' is undefined. They are seeking help to identify the error in their program and discuss potential solutions.
  • #1
ksh5022
1
0
I am writing a program to find 7 degrees of freedom, but I keep getting an error message that "the argument 'x' is undefined". Could somebody please tell me what I am doing wrong?

function dx = IMatrix(t,x,lamda,E)

I1 = 4250;
I2 = 5175;
I3 = 8397;

lamda(1) = 2/(38^.5);
lamda(2) = 5/(38^.5);
lamda(3) = 3/(38^.5);

theta = 15*(pi/180);

E(1) = lamda(1)*sin(theta/2);
E(2) = lamda(2)*sin(theta/2);
E(3) = lamda(3)*sin(theta/2);
E(4) = cos(theta/2);

x0 = [E(1) E(2) E(3) E(4) 0.2 0.7 0.4];

% Derivatives of Euler parameters represented as dx1 - dx4
dx = zeros(7,1);

dx(1) = 0.5*(x(7)*x(2) - x(6)*x(3) + x(5)*x(4));
dx(2) = 0.5*(-x(7)*x(1) + x(5)*x(3) + x(6)*x(4));
dx(3) = 0.5*(x(6)*x(1) - x(5)*x(2) + x(7)*x(4));
dx(4) = 0.5*(-x(5)*x(1) - x(6)*x(2) - x(7)*x(3));

% Derivatives of Euler Equations (w) are replaced with values dx5-dx7

dx(5) = -x(6)*x(7)*(I3-I2)/I1;
dx(6) = -x(7)*x(5)*(I1-I3)/I2;
dx(7) = -x(5)*x(6)*(I2-I1)/I3;

options = odeset('RelTol',1e-8);
[T,X] = ode45(@IMatrix,[0 60],x0,options);

fprintf('---------------------------------------------------')
fprintf('w1 w2 w3 E1 E2 E3 E4 ')
fprintf('---------------------------------------------------')
fprintf(x(1) x(2) x(3) x(4) x(5) x(6) x(7))
 
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  • #2
You wrote:
Code:
x0 = [E(1) E(2) E(3) E(4) 0.2 0.7 0.4];
Note that x0 is not the same as x. Maybe that should have been x instead of x0.
 

1. What is a 7 DOF error in MATLAB?

A 7 DOF error in MATLAB refers to a type of error that occurs when using the ode45 function, which is used to solve differential equations, with a system that has seven degrees of freedom (i.e. seven variables that change with time). This error can occur due to various reasons, such as incorrect input parameters or issues with the system itself.

2. How can I solve a 7 DOF error in MATLAB?

To solve a 7 DOF error in MATLAB, you can try the following steps:

  • Check your input parameters to make sure they are correct and appropriate for the system you are trying to solve.
  • Ensure that the system you are trying to solve is well-defined and does not have any singularities or other issues.
  • If the system involves differential equations, make sure they are properly defined and have appropriate initial conditions.
  • Consider using a different solver function, such as ode15s, which may be more suitable for certain types of systems.
  • If all else fails, seek help from experts who are familiar with MATLAB and numerical methods.

3. Can I use Ode45 to solve a 7 DOF error in MATLAB?

Yes, Ode45 is a widely used and reliable function for solving differential equations in MATLAB. However, it may not be the best option for every type of system. If you are experiencing a 7 DOF error while using Ode45, it may be worth trying a different solver function, such as ode15s, to see if it yields better results.

4. Why am I getting a 7 DOF error in MATLAB?

There could be several reasons why you are getting a 7 DOF error in MATLAB. Some common reasons include incorrect input parameters, issues with the system you are trying to solve, or problems with the solver function you are using. It is important to carefully check your code and the system you are working with to identify the cause of the error.

5. How can I get help from experts to solve a 7 DOF error in MATLAB?

If you are unable to solve a 7 DOF error in MATLAB on your own, you can seek help from experts who have experience with MATLAB and numerical methods. You can reach out to online forums, ask colleagues or classmates for assistance, or consider hiring a tutor or consultant who specializes in MATLAB. It is important to provide as much information as possible about your problem and the steps you have already taken when seeking help.

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