def METHOD_NAME(guess, test_mineral, pressures, obs_vs):
    vs = calc_shear_velocities(guess[0], guess[1], test_mineral, pressures)
    vs_l2 = [(vs[i] - obs_vs[i]) * (vs[i] - obs_vs[i]) for i in range(len(obs_vs))]
    l2_error = sum(vs_l2)
    return l2_error