The HK probability density function is a semi-infinite integral that was evaluated until recently from `0` to `np.inf`. However, after some testing, I have changed that in https://github.com/cgrima/rsr/commit/3e52d03d9191a2950c962f4f0ab8d9ddd112fbc9 from `0` to `500` because it was increasing the computation time a little bit. However, in some extreme cases with very high coherent content, it appears to be not enough. So I reverted back to the initial settings.