This command is the equivalent of the OpenGL command "glMultMatrix".
With this command you can multiply a 4x4 matrix with the current matrix (i.e. the matrix that describes the current rotation and zoom settings that will apply to any object drawn). The matrix mat must be DIMed  and have this structure:
| a0 a4 a8 a12 |
| a1 a5 a9 a13 |
| a2 a6 a10 a14 |
| a3 a7 a11 a15 |