"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)
