  This document describes the publically available numerical code
"IGMtransfer", capable of performing intergalactic radiative transfer (RT) of
light in the vicinity of the Lyman alpha (Lya) line. Calculating the RT in a
(possibly adaptively refined) grid of cells resulting from a cosmological
simulation, the code returns 1) a "transmission function", showing how the
intergalactic medium (IGM) affects the Lya line at a given redshift, and 2) the
"average transmission" of the IGM, making it useful for studying the results of
simulations of cosmic reionization.
