One of the common methods for solving the radiation transport equation is to use a polynomial expansion for the angle variable(s). While each solution technique has its disadvantages, in some instances this method can result in oscillations large enough to give a negative radiation energy density, which is nonphysical. Some authors have recast the closure of the transport equations to guarantee positivity. Unfortunately, this results in messy nonlinear equations. Other authors post process each time step’s solution to improve positivity. In this work, the P_n equations are modified to be more diffusive, less oscillatory, more positive, and more accurate. No new solution techniques are required, just the scaling of some terms with constant factors and the addition of constant filter opacities; therefore, the solutions are still linear. This new solution method is called stretched and filtered P_n. Test problems are presented in one and two dimensions. Comparisons to the D_n and TP_n closures are made in one dimension. Modifications to D_n and TP_n are suggested.

解决辐射传输方程的一种常用方法是对角度变量使用多项式展开。尽管每种解决方案技术都有其缺点，但在某些情况下，此方法可能会导致振荡足够大，从而产生非物理的负辐射能量密度。一些作者已经改写了输运方程式的闭包以保证阳性。不幸的是，这导致了混乱的非线性方程。其他作者则在每个步骤的解决方案中发布流程，以提高积极性。在这项工作中，P _n方程被修改为更具扩散性，更少振荡，更积极和更准确。不需要新的解决方案技术，仅需对具有恒定因子的某些项进行缩放，并增加恒定的滤波器不透明度即可；因此，解仍然是线性的。这种新的求解方法称为拉伸和滤波P _n。测试问题以一维和二维表示。与D _n和TP _n闭合件的比较在一维进行。建议对D _n和TP _n进行修改。