VM
The VM function calculates the magnitude of the first time derivative of the displacement vector of marker i with respect to marker j. The vector time derivative is taken in the reference frame of marker l. Markers j and l default to the global coordinate system if they are not specified.
Format
VM(i[,j][,l])
Arguments
i | The marker whose velocity is being measured. |
j | The marker with respect to which the velocity is being measured. Set j = 0, while still specifying l, if you want j to default to the global coordinate system. |
l | The reference frame in which the time derivative of the displacement vector is taken. Set l = 0 or omit the argument if you want the time derivatives to be taken in the ground coordinate system (GCS). |
Extended Definition
Mathematically, VM is calculated as follows:
where 
is the displacement of marker i in ground and 
is the displacement of marker j in ground.
is the displacement of marker i in ground and is the displacement of marker j in ground.Examples
DIFF/51, IC=-6.2, FUNCTION=VM(23,0,32)
A dynamically determined user state is defined by DIFF/51. The time derivative of the user-state is the magnitude of the velocity of the origin of Marker 23 with respect to ground. The time derivative for the velocity computation is taken in the reference frame of Marker 32.
VARIABLE/1, FUNCTION=VM(21,32,43)
This VARIABLE statement defines an algebraic, user-defined state whose instantaneous value is the magnitude of the velocity vector between Markers 21 and 32, as seen by an observer at Marker 43.
See other Velocity measures available.