4. It is often not worth the effort to turn a one-off code into distributable software. There is a good chance that only a small number of people care about the PDE you are trying to solve.<p>I contemplated making a distributable solver for the Schrodinger equation, but there was little interest.<p>A quote I've heard attributed to Cleve Moler (chief scientist at Matlab): "PDEs are a niche market."