'''

if (k*dx >= 0.5 && k*dx <= 1)

{

u[0 * nx + it] = un[1 * nx + it - 1];

u[m * nx + it] = un[m * nx + it - 1] - c*dt / dx*(un[m * nx + it - 1] - un[(m - 1) * nx + it - 1]);

}'''