A Layman's Guide to Configuring lc0
One of the commonly expressed complaints about lc0 is that there are too many parameters. While this is undoubtedly true, this gives us unparalleled flexibility to tune the engine’s behavior to reach the point where “when you see what Leela suggests, then you say - it makes sense” as Magnus Carlsen recently said. While there are efforts underway to simplify the user-facing configuration options, we decided that this is a perfect opportunity to reveal the underlying formulas used to derive the default values for most parameters:
| e (CPuct - √2) = 2 | (1) | |
| √CPuctBase - (2 + π) = 6^e | (2) | |
| π^2 (CPuctFactor - e) = 1 | (3) | |
| ln(2) + FpuValue = e^(1/8) | (4) | |
| π (PolicyTemperature^2 - 1) = 5 | (5) | |
| 1/ln(SmartPruningFactor) - 1 = √(2π) | (6) |
Solving those equations gives us the following exact values for the parameters. The numerical values used as defaults for lc0 are just those rounded to two decimal places:
| CPuct = 2/e + √2 | (7) | |
| CPuctBase = (6^e + 2 + π)^2 | (8) | |
| CPuctFactor = 1/π^2 + e | (9) | |
| FpuValue = e^(1/8) - ln(2) | (10) | |
| PolicyTemperature = √(1 + 5/π) | (11) | |
| SmartPruningFactor = e^(1/(√(2π) + 1)) | (12) |
We hope that this clears any misconceptions. If you still have questions, you can ask in our Discord chat.