Stockfish strength level

[tomitank]

Hi!

I found this:
https://github.com/niklasf/stockfish.js

This is used by "lichess".

My question is: what parameter does the "lichess" use to set engine level?

-Tamas

[Lyudmil Tsvetkov]

Hi!

I found this:
https://github.com/niklasf/stockfish.js

This is used by "lichess".

My question is: what parameter does the "lichess" use to set engine level?

-Tamas

whatever the level, it is very weak, as one is able to beat it even at level 8.

seemingly, for levels 1-6 they are using some randomisation, while levels 7 and 8 only significantly limit the time usage, to fraction of a second.

[tomitank]

That's okay.

I'm interested, for example, at level 7, what is the minimum depth and the maximum search time.

[Lyudmil Tsvetkov]

That's okay.

I'm interested, for example, at level 7, what is the minimum depth and the maximum search time.

that will depend on the computers.

as different users will be served by different cpus, depth will vary.

[tomitank]

I do not think so.

On weaker devices, it searched longer.

[tomitank]

From stockfish source code:

Code: Select all

#ifdef SKILL
  // Skill structure is used to implement strength limit
  struct Skill {
    Skill(int l) : level(l) {}
    bool enabled&#40;) const &#123; return level < 20; &#125;
    bool time_to_pick&#40;Depth depth&#41; const &#123; return depth / ONE_PLY == 1 + level; &#125;
    Move best_move&#40;size_t multiPV&#41; &#123; return best ? best &#58; pick_best&#40;multiPV&#41;; &#125;
    Move pick_best&#40;size_t multiPV&#41;;

    int level;
    Move best = MOVE_NONE;
  &#125;;
#endif

Code: Select all

      // If skill level is enabled and time is up, pick a sub-optimal best move
#ifdef SKILL
      if (skill_.enabled() && skill_.time_to_pick(rootDepth))
          skill_.pick_best(multiPV_);
#endif

Accordingly, is the set level + 1 equal to the maximum search depth?

[Fabian Fichter]

You can find the relevant code for the settings of movetime, depth limit, and skill level here:
https://github.com/niklasf/fishnet/blob ... #L109-L110
https://github.com/niklasf/fishnet/blob ... #L774-L782

[Vinvin]

From stockfish source code:

Code: Select all

#ifdef SKILL
  // Skill structure is used to implement strength limit
  struct Skill {
    Skill(int l) : level(l) {}
    bool enabled&#40;) const &#123; return level < 20; &#125;
    bool time_to_pick&#40;Depth depth&#41; const &#123; return depth / ONE_PLY == 1 + level; &#125;
    Move best_move&#40;size_t multiPV&#41; &#123; return best ? best &#58; pick_best&#40;multiPV&#41;; &#125;
    Move pick_best&#40;size_t multiPV&#41;;

    int level;
    Move best = MOVE_NONE;
  &#125;;
#endif

Code: Select all

      // If skill level is enabled and time is up, pick a sub-optimal best move
#ifdef SKILL
      if (skill_.enabled() && skill_.time_to_pick(rootDepth))
          skill_.pick_best(multiPV_);
#endif

Accordingly, is the set level + 1 equal to the maximum search depth?

Yes, SF level on Lichess is 1 to 8. "1" is the strongest level, I think it search for 2 millions nodes or so.
Other levels are simply a constant progression to map "1 to 8" to "1 to 20 SF levels".

[tomitank]

Is correct?

At Level 8: Max depth = 62, movetime = 370ms / thread (default 3)
At Level 7: Max depth = 37, movetime = 185ms / thread (default 3)