def phi_analytic(dist, t, t_0, k, phi_1, phi_2):
    phi = (phi_2 - phi_1)*(t_0/(t + t_0))* \
        numpy.exp(-0.25*dist**2/(k*(t + t_0)) ) + phi_1
    return phi
the analytic solution to the Gaussian diffusion problem
dataset/ETHPy150Open zingale/pyro2/diffusion/problems/gaussian.py/phi_analytic