Functional derivative
= Functional derivative
{title2=$\delta F/\delta\phi$}
{wiki}
The functional derivative is defined by the first variation
$$
F[\phi+\epsilon h]-F[\phi]
=\epsilon\int\frac{\delta F}{\delta\phi(x)}h(x),dx+o(\epsilon).
$$
= Functional derivative
{title2=$\delta F/\delta\phi$}
{wiki}
The functional derivative is defined by the first variation
$$
F[\phi+\epsilon h]-F[\phi]
=\epsilon\int\frac{\delta F}{\delta\phi(x)}h(x),dx+o(\epsilon).
$$