pdsolveComesUpWithComplexResult.mw

I'm struggling to get a simple answer out of pdsolve solving this PDE:  

eqn := Mu*diff(`ξr`(r, t), t, t) = kappa*diff(`ξr`(r, t), r, r);
ic := `ξr`(r, 0) = sin(Pi/(2*r)), D[2](`ξr`)(r, 0) = 0;
bc := `ξr`(0, t) = 0, D[1](`ξr`)(1, t) = 0;
sol := (pdsolve([eqn, ic, bc], Zeta(r, t)) assuming (0 < kappa, 0 < Mu));

The outcome pdsolve comes up with is rather complex, with summation and integral. To my best knowledge, the simple solution of this PDE is:

sin(Pi*r/2)*cos(1/2*sqrt(k/m)*Pi*t)

How can I get this simple solution out of pdsolve? 

Any suggestion is welcome.

Wouter
 

Download HowToDefineTensorRankZero.mw

Using the latest Physics package, I try define a tensor of rank zero, but an error accurs:

> Define(Theta = varepsilon[mu, ~mu](X));
Error, (in Physics:-Define) expected left-hand-side of tensor definition as a tensor with non-numerical indices, received: Theta

The same error occurs when I try:
> Define(Theta[] = varepsilon[mu, ~mu](X));
Error, (in Physics:-Define) expected left-hand-side of tensor definition as a tensor with non-numerical indices, received: Theta[]

So my question is: how can I define a tensor of rank zero? 
Hope someone can help me out. 

Regards, Wouter