FR: Volume Preserving Real NVP Variant (GIN)

Hi all,

I noticed that Real-NVP has an option for "Volume Preserving", but this just omits the scale factors, and performs the NICE transform. Would it be possible to implement a more powerful volume preserving transformation (I need it for a specific purpose) by simply modifying Real-NVP so the final scale variable is the negative sum of the others?

The very simple idea can be found in this ICLR2020 paper: https://arxiv.org/abs/2001.04872

Similarly, it should be possible to do this for IAF.

It should be easy for someone who is familiar with the code already.