Prismatic
=========

A prismatic joint creates a point that is translated relative to an existing point with vector components defined in a specified reference frame. The joint is analogous to creating a vector and point using the classic interface. The vector component can be constant valued, or a degree of freedom (DOF) may be generated where the point can translate in the unit vector direction. If the DOF form is chosen, then an optional linear stiffness, damping, and equilibrium distance can be used to include translational spring-damper physics in the joint.

**Keyword Arguments**

:param str name: Name given to the joint, default is uppercase characters in alphabetical order (A, B, C, ...)

:param str ref_point_key: Start point from which the vector component of the joint is defined

:param str ref_frame_key: Reference frame in which the components of the vector are defined, with basis vectors e_x, e_y, and e_z

:param str is_form: 'constant' or 'degree of freedom'

**Vector Components**

:param numeric x: Component of the unit vector measured in the x-axis of the reference frame

:param numeric y: Component of the unit vector measured in the y-axis of the reference frame

:param numeric z: Component of the unit vector measured in the z-axis of the reference frame

**Initial States**

:param numeric value: Initial value for the generalized coordinate if is_form == 'degree of freedom'

:param numeric rate: Initial value for the generalized speed if is_form == 'degree of freedom'

**Spring Parameters**

:param numeric k: Spring constant

:param numeric c: Damping constant

:param numeric equilibrium: Equilibrium distance

:return str: Message describing the inputs used in creation of the joint