Variational Principles in Physics: From Classical to Quantum Realm (SpringerBriefs in Physics)
Variational Principles in Physics: From Classical to Quantum Realm (SpringerBriefs in Physics),Variational Principles of Continuum Mechanics: I. Fundamentals | SpringerLink,(#5): Variational Method: simple example,partial differential equations - Theorem $2$ (Variational principle for the principal eigenvalue) - Mathematics Stack Exchange,partial differential equations - Theorem $2$ (Variational principle for the principal eigenvalue) - Mathematics Stack Exchange