def METHOD_NAME(eta, u, v, h):
    """Solves w from continuity equation"""
    div_uv = sympy.diff(u, x) + sympy.diff(v, y)
    c = u*sympy.diff(h, x) + v*sympy.diff(h, y)
    w = -sympy.integrate(div_uv, (z, -h, z)) - c
    return w