'Domain error. To compute complex results from real x, use 'acos(complex(x))' error in matlab?

hi.i want to simulate ur10 inverse kinematic and I did it.while running there is this error:

Domain error. To compute complex results from real x, use 'acos(complex(x))

how can I fix it?

the error is general and I don't know which line should be changed. there are several acos in the code .

X is the endeffector position and it can not be complex.

I have attached the Simulink file.

[Walter Roberson]

Change them all.

[Sebastian Castro]

Unfortunately, "changing them all" wouldn't help in this case.

It actually doesn't have to do with the input being complex, but rather the input being outside the real valued range [-1,1] of the cos function.

Refer to my Answer below.

Answer 1

[Sebastian Castro]

Hi Najmeh,

If you supply a value greater than 1 or smaller than -1 to the acos function, you get a complex number. Simulink seems to be complaining about that in your code.

Theta5=acos(argumancos5);%negetive or positive answer?

Seems like at the very first time step, argumancos5 is exactly 1, but due to numerical issues, it's actually slightly higher than 1 which leads to your error. Computing the value argumancos5 - 1 gives me 3.1086e-15... so it's just outside the range in which the cosine is real-valued.

I limited the value of this input to the range [-1, 1] and it seems to have fixed the error:

argumancos5 = max(min(argumancos5,1),-1);
Theta5=acos();%negetive or positive answer?

- Sebastian

[Najmeh Eskandari]

yes. Error resolved but e123 and e456 are too large. I changed all acos to acos(complex(x)) then deleted complex one by one. I guess the error is related to Theta3.

[Najmeh Eskandari]

I analysed the kinematic according to the following PDF.

[Sebastian Castro]

Right, so we established the error was because passing a value outside the range [-1,1] produces a complex output to acos... so you shouldn't need to pass in complex(x) if you ensure your inputs are bounded.

If the errors are large, my guess is you need to debug your code and make sure it's correct!

[Gautami Golani]

Hey Najmeh,

Were you able to resolve this issue?

I'm currently simulating the inverse kinematics of the UR5 and facing the same problem.

Any help would be appreciated.

[Moussa LABBADI]

Thank you.

[Aks Lyu]

This is the answer!

But why MATLAB does not point out which line (file) the error occures in?

[superman]

Awesome！