Return values for use outside of function

[buran]

your function returns uVector (no need of the brackets, by the way) and you assign the value returned by the function to systemResponse. You must use that name, not uVector (which is local to function scope only, i.e. it doesn't exists outside the function).
By the way, instead of systemResponse you can use uVector, without any problem, if that name is more meaningful, e.g.

uVector = calculateResponse(tvector, f2vector, f3vector)