Position TRACK_PROBE_X(R,X,K, FIBRE1,FIBRE2,NODE1,NODE2)

• R is a LAYOUT,
• X is an array of initial conditions and final upon return.
• K is an INTERNAL_STATE.
• FIBRE1,FIBRE2,NODE1,NODE2 are all integers.
• Here one specifies the initial FIBRE position in FIBRE1 and the program tracks to the front of FIBRE2
• FIBRE2 is optional. If not there, tracking continues all the way to the front of FIBRE1 or to a terminated FIBRE pointer.
• Here one specifies the initial NODE1 and the program tracks to the front of NODE2
• NODE2 is optional. If not there, tracking continues all the way to the front of NODE1 or to a terminated NODE pointer.

Nodes and Fibres are mixable. For example, TRACK_PROBE_X(R,X,K, FIBRE1=p1,NODE2=n2) is acceptable.