An orthogonalization process is proposed, applicable to spaces which are realizations of abstract Hilbert space. It is simpler than the Gram-Schmidt process. A recurrence relation which orthogonalizes a physical space is proposed and it is shown that the generalized Langevin equation is contained therein. This process serves as a basis for understanding the nature of the dynamic many-body formalism.

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By the method of recurrence relations, the time evolution in a local variable in a harmonic chain is obtained. In particular, the autocorrelation function is obtained analytically. Using this result, a number of important dynamical quantities are obtained, including the memory function of the generalized Langevin equation. Also studied are the ergodicity and chaos in a local dynamical variable.