Coordinate system
"Optional title"
csysid, $x_0$, $y_0$, $z_0$, pid
$\hat{x}_x$, $\hat{x}_y$, $\hat{x}_z$, $\bar{y}_x$, $\bar{y}_y$, $\bar{y}_z$
Parameter definition
csysid Unique identification number
$x_0$, $y_0$, $z_0$ Initial coordinate of origin
pid Optional part ID
default: not used
$\hat{x}_x$, $\hat{x}_y$, $\hat{x}_z$ Initial direction of local x-axis
$\bar{y}_x$, $\bar{y}_y$, $\bar{y}_z$ Vector needed for the definition of the local y- and z-axis

This command defines a local cartesian coordinate system. The system is forced to follow the translation and rotation of the finite element in which it is embedded at time 0 (Lagrangian description of motion). Hence, the origin of the system must be located on the surface of, or embedded inside, the finite element mesh.

The origin is initially located at ($x_0$, $y_0$, $z_0$) and the local x-direction is ($\hat{x}_x$, $\hat{x}_y$, $\hat{x}_z$). The local z-direction is defined as $\hat{\mathbf{z}} = \hat{\mathbf{x}} \times \bar{\mathbf{y}} / \vert \hat{\mathbf{x}} \times \bar{\mathbf{y}} \vert$ and the local y-direction as $\hat{\mathbf{y}} = \hat{\mathbf{z}} \times \hat{\mathbf{x}}$.

The part ID (pid) is only needed when the initial location of the origin is right in the boundary between two different parts and when the system needs to be tied to one of these parts.

Note that, for fixed (Eulerian) coordinate systems, there is a special command COORDINATE_SYSTEM_FIXED.