def _calc_RMSD(x0, y, ppm, spins):
x0 = np.ndarray.tolist(x0)
ls = np.zeros_like(ppm)
for i, s in enumerate(spins):
s.set_opt_vals(x0)
if i == 0: ls += Shapes.logistic_basline(ppm, s)
else: ls += Shapes.Gaussian(ppm, s)
return np.linalg.norm(y - ls)
