We have approximated the special Kin(X) functions used in formulas for radiation character: istics. We have found the approximate intermediate functions for an isotropic incident flow by means of which [2] many angle factors have been expressed. w i. Introduction Two-dimensional systems of bodies with an absorbing medium exhibit comparitively simple radiation characteristics. For the isotropic radiation of surfaces, Mikk has examined the angle factors in a number of papers [1][2][3]. Many of the factors are determined by means of the intermediate functions M, Ni, N2, and $2, and these in turn are expressed in terms of the tabulated Bessel functions and their integrals. The radiation characteristics have been generalized in [4] for the axisymmetric indicatrix of effective surface radiation, given by a series in cosines. The formulas have been simplified by using the special Kin(X) functions in the place of the Bessel functions. Moreover, the above-cited reference enumerates most fully the properties of the Kin functions. The difficulties are now reduced to the calculations of the Kin functions. Tables of these functions are not readily accessible and they are limited.To use an electronic digital computer, particularly machines of the Promin and Nairi types, the functions must be approximated by simple formulas. Here we offer approximate Kin functions whose derivatives are intermediate functions, and we give important examples of the approximation of angle factors.The original formulas are taken in two variants:The integrals are replaced by quadrature formulas Kia(x) ~.~ ~a t exp (--b,x).m As the first approximation the coefficients ai and b i are determined from the weights and nodes of the Gauss quadrature. As a rule, the coefficients a i are then increased and simultaneously rounded off to satisfy the equation
