Solve wave equation with PDEPE function

Hello everyone,

I would like to use pdepe for solving a wave equation 1D space (d2y/dx2 = C*d2y/dt2), so it looks good. But I don't really understand where the diffusion coefficient is ?

But I'm really not understanding how to use the PDEPE function, all the examples I see, the equation is different (dy/dx = C*d2y/dt2).

Thanks for all...