The article by Robert J. Guyan discusses the reduction of stiffness and mass matrices in structural analysis, particularly for natural mode analysis. The author proposes a technique similar to the one used for stiffness matrices, which involves eliminating coordinates where no forces are applied. This process results in a reduced stiffness matrix \( K_1 \) and a reduced mass matrix \( M_1 \). The reduced stiffness matrix is derived from the original stiffness matrix through a coordinate transformation, while the reduced mass matrix is obtained by combining stiffness and mass elements. The eigenvalue-eigenvector problem is preserved but not exactly, as some combinations of stiffness and mass elements appear in the reduced mass matrix. Comparative results for beam vibrations are reported in a reference by Archer (1963).The article by Robert J. Guyan discusses the reduction of stiffness and mass matrices in structural analysis, particularly for natural mode analysis. The author proposes a technique similar to the one used for stiffness matrices, which involves eliminating coordinates where no forces are applied. This process results in a reduced stiffness matrix \( K_1 \) and a reduced mass matrix \( M_1 \). The reduced stiffness matrix is derived from the original stiffness matrix through a coordinate transformation, while the reduced mass matrix is obtained by combining stiffness and mass elements. The eigenvalue-eigenvector problem is preserved but not exactly, as some combinations of stiffness and mass elements appear in the reduced mass matrix. Comparative results for beam vibrations are reported in a reference by Archer (1963).