BesselI[n, z] gives the modified Bessel function of the first kind .
Mathematical function (see Section A.3.10).
satisfies the differential equation .
BesselI[n, z] has a branch cut discontinuity in the complex z plane running from to .
FullSimplify and FunctionExpand include transformation rules for BesselI.
See The Mathematica Book: Section 3.2.10.
See also: BesselK, AiryBi, BesselJ.