NB. Hydrogenic recombination coefficients NB. Usage: a_rad (T,Z) a_rad=: monad define 'T Z'=. y C =. 2.065e_13*Z*Z% %:t=. 1e_4*T lam=. 15.789*Z*Z%t alph=. C*0.4288+(-: ^.lam)+0.469%lam^(%3) alphdt=. (- -:alph%t)+C*((0.469%lam^%3)%3*t)- %2*t alph, 1e_4*alphdt )