MATLAB Answers


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

Najmeh Eskandari さんによって質問されました 2018 年 8 月 11 日
最新アクティビティ Aks Lyu
さんによって コメントされました 2019 年 12 月 11 日 5:20
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.

  2 件のコメント

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.

サインイン to comment.

1 件の回答

Answer by Sebastian Castro on 13 Aug 2018
Edited by Sebastian Castro on 13 Aug 2018
 Accepted Answer

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

  6 件のコメント

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.
This is the answer!
But why MATLAB does not point out which line (file) the error occures in?

サインイン to comment.

Translated by