MATLAB: ‘Domain error. To compute complex results from real x, use ‘acos(complex(x))’ error in matlab

Question

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.

Answer 1

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