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For reasons explained in Chapter I, our studies have so far been confined to linear systems


with symmetric and positive definite coefficient matrix A. b is the vector of the constant terms, x is the vector of the unknowns, but in this chapter, the letter x shall denote an arbitrary point of the N- dimensional space whereas the solution of (II. 1) will be denoted by — A-1b. The order of the system will be denoted throughout by JV, whereas n is used for the number of different eigenvalues of A, which may be smaller than N.