// Behavior.
const real MARGIN = 0.01;

automaton machine:
  cont rate der if rate < target_rate:  1.0
                else                   -1.0
                end;
  disc real target_rate = 0.5;
  disc dist real rate_sampler = uniform(0.0, 1.0);

  location:
    initial;
    edge when rate - MARGIN <= target_rate and target_rate <= rate + MARGIN
         do (target_rate, rate_sampler) := sample rate_sampler;
end

// Visualization.
svgfile "rate.svg";

svgout id "circle_bg_rect" attr "height"
  value scale(machine.rate, 0, 1, 58, 0);

svgout id "circle_bg_rect" attr "fill" value "white";