= Free-energy functional
{title2=$\mathcal A[m]$}
A <free-energy functional> assigns a <free energy> to an entire spatial <order parameter> configuration rather than only to one uniform value. In <Landau-Ginzburg theory>, a <local derivative expansion> gives $\mathcal A[m]=\int d^Dx\{\kappa(\nabla m)^2/2+V(m)\}$, with appropriate boundary terms and regular backgrounds. The <Landau approximation> minimizes this functional; a fluctuating <statistical field theory> instead integrates its <Boltzmann weight> over configurations. These procedures need not give identical <critical exponents>.
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