I dunno, it's a lot more difficult, since you got a function of 2 variables, B & xi. Maybe you can fix xi to a certain value (one which is considered in the table) and then try to interpolate for an arbitrary value of B inside the intervals.
Daniel.
About transcendental functions: those polynomial functions must have algebraic numbers as coefficients. Thus, a polynomial function with transcendental coefficients is a transcendental function.
Daniel.