  The structure of weighting coefficient matrices of Harmonic Differential
Quadrature (HDQ) is found to be either centrosymmetric or skew centrosymmetric
depending on the order of the corresponding derivatives. The properties of both
matrices are briefly discussed in this paper. It is noted that the
computational effort of the harmonic quadrature for some problems can be
further reduced up to 75 per cent by using the properties of the
above-mentioned matrices.
