This letter shows 50 percent memory saving for a regular Hierarchal Matrix (H-matrix) by converting it to symmetric H-matrix for large electrodynamic problems. Only the upper diagonal near-field and compressed far-field matrix blocks of the H-matrix are stored. Far-field memory saving is achieved by computing and keeping the upper diagonal far-field blocks leading to compressed column block U and row block V at a level. Due to symmetry, the lower diagonal far-field H-matrix compressed column is the transpose of V, and the compressed row block is the transpose of U. Storage and computation of lower diagonal blocks are not required. Similarly, in the case of near-field, only the upper diagonal near-field blocks are computed and stored. Numerical results show that the proposed memory reduction procedure retains the accuracy and cost of regular H-matrix.
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