Would you kind help me? I am an undergraduate student and i am studying about variational iteration method (VIM) by Ji Huan He. But, when i study about the stationary condition of VIM, there is a functional :
$$J=\int_{x_1}^{x_2} F(y,y';x) dx + g_1(x)y|_{x=x_1}-g_2(x)y|_{x=x_2}$$
In the functional there are function $g_1(x)$ and $g_2(x)$. But no explanation about the kind of that function. The text just says that $y=f(x)$. Does someone know the kind of $g_1(x)$ and $g_2(x)$ ? Thank you in advance