There are not exact solutions. Instead, you can setup enumerous Nx for WENO-Z as exact solution. [1] G.S. Jiang, C.W. Shu, Efficient implementation of weighted ENO ...

This project is a pixel-by-pixel Stokes inversion code written in C and paralleled with MPI, follows the analytic solutions described in Introduction to Spectropolarimetry by J. C. del Toro Iniesta ...