Troubleshooting MathCAD: Rotation of Body Vector About an Axis

[TheJCBand]

I'm not sure if this is the right place for this question, but I didn't see a forum specifically about software.

I'm trying to define a function in MathCAD that describes the rotation of a body vector about an axis u by an angle ɸ. What I've typed in is:

R(ɸ,u):= [ 3x3 matrix where each element is a function of ɸ and u ]

When I try evaluating the function for a given ɸ and u, it gives me the error "This array index is invalid for this array."
It sounds like the program thinks the parentheses indicate a an array index instead of the arguments of the function. Does anyone have any suggestions?

Thanks.

 

[TheJCBand]

I figured out the problem. My function R used indexes of the vector u, and the first index is 0 in MathCAD, and I using 1, so there was a u₃ in the function, which didn't exist.