I’m reading the devito_book/fdm-jupyter-book/notebooks/01_vib/vib_undamped.ipynb and the code in it seems not compatible with devito 4.8.3.

So I tried to rewrite it as:

import numpy as np
from devito import Constant, TimeFunction, Eq, solve, Operator, Grid, TimeDimension


def solver(I, w, dt, T):
    dt = float(dt)
    Nt = int(round(T / dt))
    t = TimeDimension('t', spacing=Constant('h_t'))
    grid = Grid(shape=(Nt + 1, ), time_dimension=t)
    u = TimeFunction(name='u', grid=grid, time_order=2)

    u.data[:] = I
    eqn = u.dt2 + w ** 2 * u
    stencil = Eq(u.forward, solve(eqn, u.forward))
    op = Operator(stencil)
    op.apply(h_t=dt, t_M=Nt - 1)
    return u.data, np.linspace(0, Nt * dt, Nt + 1)


I = 1
w = 2 * np.pi
dt = 0.05
num_periods = 5
P = 2 * np.pi / w
T = P * num_periods
u, t = solver(I, w, dt, T)

However, the data of returned u is:

[[0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113 0.95374113,  0.95374113 0.95374113 0.95374113 0.95374113 0.95374113], [1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983,  1.0121983  1.0121983  1.0121983  1.0121983  1.0121983 ], [0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535,  0.8011535  0.8011535  0.8011535  0.8011535  0.8011535 ]]

The value does not update from one time node to the next. Could anyone help me solve this issue?

Thank you in advance!