| Matrix or Vector | Shape Functions | Integration Points |
|---|---|---|
| Mass Matrix | None | None |
In the element coordinate system, the element mass matrix is:
 | (13–17) |
where:
 |
| ρ = density (input as DENS on MP command) |
where a', b', c', d', e', f', x0, y0, and z0 are user input (input on the R command) in the locations shown in the following table:
| KEYOPT(3) = 0 | KEYOPT(3) = 2 | KEYOPT(3) = 3 | KEYOPT(3) = 4 | |
|---|---|---|---|---|
| a' | 1 | 1 | 1 | 1 |
| b' | 2 | 1 | 1 | 1 |
| c' | 3 | 1 | - | - |
| d' | 4 | - | - | - |
| e' | 5 | - | - | - |
| f' | 6 | - | 2 | - |
| x0 | 8 | - | - | - |
| y0 | 9 | - | - | - |
| z0 | 10 | - | - | - |
For the mass summary, only the first real constant is used, regardless of which option of KEYOPT(3) is used. The precise mass summary used for three-dimensional models as well as analyses with inertial relief use the complete matrix.