code: def _rhoTilde(self, r, N,L):
          
          xi = self._calculateXi(r)
          CC = _C(xi,N,L)
          a = self._a
          rho = nu.zeros((N,L), float)
          n = nu.arange(0,N, dtype=float)[:, nu.newaxis]
          l = nu.arange(0, L, dtype=float)[nu.newaxis,:]
          K = 0.5 * n * (n + 4*l + 3) + (l + 1.)*(2*l + 1)
          rho[:,:] = K * ((a*r)**l) / ((r/a)*(a + r)**(2*l + 3.)) * CC[:,:]* (nu.pi)**-0.5
          return rho
docs: NAME:
             _rhoTilde
          PURPOSE:
             Evaluate rho_tilde as defined in equation 3.9 and 2.24 for 0 <= n < N and 0 <= l < L
          INPUT:
             r - Evaluate at radius r
             N - size of the N dimension
             L - size of the L dimension
          OUTPUT:
             rho tilde 
          HISTORY:
             2016-05-17 - Written - Aladdin