---

def pyass(nx, nt, hx, ht, f, U_st):
    U_nov = U_st.copy()
    #метод простой итерации
    for i in range(1, nx - 1):
        for j in range(1, nt - 1):
            U_nov[i][j] = (((U_st[i-1][j] + U_st[i+1][j])/hx**2) + ((U_st[i][j-1] + U_st[i][j+1])/ht**2) - f)/((2/hx**2) + (2/ht**2))
    return U_nov