Hu–Washizu principle

In continuum mechanics, and in particular in finite element analysis, the Hu–Washizu principle is a variational principle which says that the action


 * $$\int_{V^e} \left[ \frac{1}{2} \varepsilon^T C \varepsilon - \sigma^T \varepsilon + \sigma^T (\nabla u) - \bar{p}^T u \right] dV - \int_{S_\sigma^e} \bar{T}^T u\ dS$$

is stationary, where $$C$$ is the elastic stiffness tensor. The Hu–Washizu principle is used to develop mixed finite element methods. The principle is named after Hu Haichang and Kyūichirō Washizu.