BESSEL FUNCTION

[Bes.sel function] n [Friedrich W. Bessel d. 1846 Prussian astronomer] (1872): one of a class of transcendental functions that are expressible as the sum of an infinite series and that occur in the solution of the differential equation for which the left side consists of the sum of two terms of which one is the square of the independent variable x times the second derivative with respect to x and the other consists of x times the first derivative with respect to x and the right side consists of the dependent variable y multiplied by the difference between the square of n and the square of x