---

# Теплопроводность явная схема
def puas(nx, nt, hx, ht, f, u_old):
    u_new = u_old.copy()
    for i in range(1, nx-1):
        for j in range(1, nt-1):
            u_new[i][j] = u_old[i][j-1] + k*(u_old[i-1][j-1] - 2*u_old[i][j-1] + u_old[i+1][j-1])+ht*f
    return u_new