Documentation: rng_seed

[Robinlovelace]

Just discovered this by searching for 'rng' in the repo.

I tried to generate reproducible networks in https://github.com/acteng/netgen/pull/22/commits/f31cf84dfd4d6eccd9b8eb3e968302a3a53fb35d but, having re-run

sudo docker run -v $(pwd):/app ghcr.io/urban-analytics-technology-platform/od2net:main /app/config.json

and comparing the results with

diff /tmp/output.geojson output/output.geojson

After copying the previous version it seems there are still differences.

Probably worth documenting and happy to give it a go, after I figure it out myself.

[dabreegster]

If you don't pass any value, it defaults to a fixed value of 42. If you run on the same input twice, you should get the same output. The only difference between the two runs is some caching in the intermediate directory, but it shouldn't cause any changes

[Robinlovelace]

Oh! I could have sworn outputs were changing from one run to another, but maybe I'm changing something..