Formulation of the element matrices and vectors for elasticity problem

The total system matrix (global stiffness matrix) is symmetrical provided its constituent matrices are symmetrical. The matrix also possesses the useful property of "bandedness" which means that the terms are concentrated around the "leading diagonal". This symmetry is also taken into account. The symmetrical half of a band matrix is stored as a rectangular array with a size equal to the number of system equations times the semi-bandwidth plus 1. In this case zeros are filled into the extra locations in the first few or last rows depending on whether the lower or upper "half" of the matrix is stored. Special storage scheme, the "skyline" technique is also implemented. To reduce storage requirements this technique is recommended. This has the effect of reducing the number of zero terms that would be stored in the stiffness matrix due to bandwidth variability using conventional (constant bandwidth) storage methods.