Note on magnetic vector potential A.
The components of the magnetic vector potential A can be output, either before ray tracing (using the option ‘along a line or arc of a circle’) or after ray tracing. One occasion when it is useful to see the components of A is in designing a 'magnetic angle changing' device, as explained in the 17th example file.
The magnetic vector potential A is indefinite, in the sense that adding the gradient of any function to it does not change the value of the magnetic field derived from A (because curl(grad V) = 0). In CPO3D we have chosen to use the simplest and most obvious expressions for A, giving:
(1) A = 0 at the origin of coordinates, for a uniform B,
(2) A = 0 at the centre of a circular loop of current.
The units of A are the SI unit Tesla.m.