that we can achieve between $0.1$ and $1$ percent relative error in the solution, and with several orders of magnitude fewer parameters than a standard multigroup formulation using Planck-weighted opacities for a comparable accuracy.
author:
- |
    T. S. Haut and C. Ahrens and A. Jonko and R. Lowrie and A. Till\
    Los Alamos National Laboratory\
    Los Alamos, NM 87545
bibliography:
- 'opacity\_averaging.bib'
title: 'A new multigroup method for cross-sections that vary rapidly in energy'
---

Background
==========

Thermal radiative transfer (TRT) plays a key role in a number of scientific and engineering disciplines. For example, resolving the radiation field in three-dimensional cloudy atmospheres is key to understanding a number of atmospheric science and remote sensing problems [@MAR-DAV:2005]. In many TRT problems, there is rapid variation in the opacity with energy (or frequency) due to bound-bound and bound-free transitions. In fact, for broad-band TRT problems there can be hundreds of thousands of absorption lines, whose widths are many times smaller than the overall energy range of interest. This fine scale structure in the opacities, coupled with discretizing the spatial and angular variables, places large demands on computational resources. Thus, researchers have sought methods to “average” or “homogenize” the opacities and 