Comment on 'Lagrange-multiplier method in correlated-electron systems: Exact diagonalization study'

We discuss the Lagrange-multiplier method in a many-body system, and how to apply the Lagrange multiplier correctly to realize quantum constraint in a Hamiltonian for a quantum system. It is pointed out that the discussion in Yanagisawa’s paper [Phys. Rev. B 57, 6208 (1998)] lacks a basic knowledge of mathematics, and that his conclusion is generally wrong.published_or_final_versio