Why do I get an "Unrecognized function or variable 'slerp'" error when calling "slerp"

I am getting an "Unrecognized function or variable 'slerp'" error when calling "slerp". When I use "which slerp" or "which -all slerp" from the command window, MATLAB returns "'slerp' not found." Additionally, we can find the documentation for "slerp" by searching for it, but we cannot find the function listed under any of the toolbox pages that it is a part of (Robotics Systems, Navigation, Sensor Fusion and Tracking, etc.)

Here is the code that is used to call "slerp":

q0 = eul2quat([0,0,0]); 
q1 = eul2quat([pi/2,pi/4,pi/6]);
slerp(q0,q1,.5) 

Answer 1

[MathWorks Support Team]

"Slerp" is a method of the quaternion class, not a function. Since "slerp" is a method, it will not be on the path. Once the quaternion object is loaded into MATLAB's memory (typically by constructing it), MATLAB loads the methods of the quaternion class. At this point, "which -all slerp" would find the method. 

In the code in your question, the N-by-4 arrays produced by "eul2quat" are passed to "slerp" as arguments. However, "slerp" only accepts quaternion objects as arguments. Since the quaternion objects are never constructed, the "slerp" function is never loaded. 

For this case, there are two potential workflows to achieve the desired result:

1) Use the “quaternion” function to create quaternion objects

Using the “quaternion” function instead of the “eul2quat” function will solve the issue. The code snippet below shows an example that provides the same functionality as the code in your question.

q0 = quaternion([0 0 0], 'euler', 'ZYX', 'frame');
q1 = quaternion([pi/2, pi/4, pi/6], 'euler', 'ZYX', 'frame');
slerp(q0,q1,.5)

2) Use "eul2quat" and then create quaternion objects

If you would prefer to use the “eul2quat” function, you can build a quaternion object from the output before calling the "slerp" method. Please see the code snippet below for an example using this workflow.

x0 = eul2quat([0,0,0]);
x1 = eul2quat([pi/2,pi/4,pi/6]);
q0 = quaternion(x0);
q1 = quaternion(x1);
slerp(q0,q1,.5)