Approximation of the error function, $${\rm erf}(z) = \frac{2}{\sqrt{\pi}}\int_{-\infty}^{z}\!{\rm d}x\,{\rm e}^{-x^2},$$ using elementary functions could be useful, particularly for PDC and spatial walk-off simulations…
Wikipedia, Sergei Winitzki’s paper
Erf function approximation