:::Input definition:::
a1 = inner radius of the solenoid coil.
a2 = outer radius of the solenoid coil.
b1 = bottom-most location of the solenoid coil.
b2 = upper-most location of the solenoid coil.
I = operation current of the solenoid coil.
n = total number of turns in the solenoid coil.
r = radial location of interested point.
z = axial location of interested point.
:::Output definition:::
Bz = axial field at the location.
Br = radial field at the location.
:::Warnings:::
There is no input parameter guard for now. Do not try to calculate with wrong input such as a2 < a1 cases.
Good luck with your magnet!
::::::Made by Wooseung Lee (wooseung@mit.edu)::::::