SGDym 0.2.0 'distance' mean

[CuiCG]

Environment details

If you are already running SDGym, please indicate the following details about the environment in which you are running it:

• SDGym version:0.2.0
• Python version:3.7
• Operating System:linux

Problem description

in 0.2.0 version sgdym/evaluate.py what's mean in function _compute_distance? can you explain it ,especially for distance_c

What I already tried

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If there was a crash, please include the traceback here.