[danbruc]

Why is that cheating? But it is still very slow, I got it down to 0.42 seconds.

  function controlFunction(block)
  {
    const t = Math.round(block.T / 0.02);

    return (t <= 10) ? +50
         : (t <= 18) ? -50
         : (t == 19) ? -22.4538198550841
         : (t == 20) ? -27.5461801449159
         :               0;
  }

Misses the target by 6.1E-16 at an velocity of 6.3E-15. But yes, this should probably randomize the initial conditions or parameters like friction and gravity a bit so that you actually have to control the system.

[ssl232]

It's cheating because real world PID controllers only apply linear feedback, i.e. feedback expressed by a linear function. Ifs/elses etc. are not linear.

[danbruc]

PID controller only appears in the Hacker News title, the URL just says control challenge. Also, why would you allow people to write arbitrary code if you just wanted a PID controller, then you should just allow them tuning the parameters and not write the complete thing themselves.

[ssl232]

True. I'd still argue it's not realistic to use arbitrary code though, as most control problems need linear or at least invertible control laws, and the analysis techniques that provide you with control solutions usually assume so too.

[danbruc]

I have no real clue about control theory, what is the advantage of linear or invertible laws?

My idea was to equip the control program with the equations of the system and some unknown parameters for friction and so on. Then estimate the parameters from the response to control inputs and drive the system through state space as hard as possible to get the fastest time, taking into account deviations from the expected state and reestimating parameters each time step. Would be really interested in knowing whether this could work or if this will just consistently slam into a wall. Response delay would probably make this a lot harder, but I did not look if any of the tasks simulates delays.

[BOOSTERHIDROGEN]

Stability: Adaptive control algorithms need to ensure stability while adapting to changing parameters. This can be a complex task, and stability guarantees are essential.