let a = 0, r = 300;
        let theta = 0.0;

        function setup() {
          createCanvas(300, 300);
        }

        function draw() {
          background(0, 15);
          a = Math.abs(sin(theta));
          let y = map(sin(theta), -1, 1, 15, height - 15);
          fill(255, 0, 200, 50)
          noStroke();
          ellipse(width / 2, height / 2, a * r, a * r);
          theta += 0.1;
        }