When the following code is run, a sphere moves in a curve from the middle of the screen to the top, but I'm trying to make it function so that the peak (highest point) of the curve is in the center of the screen. Does anyone have any idea where I'm going wrong? Thanks in advance!

1. float t;
2. float a = 0.0;
3. 
   
4. void setup(){
5.   size(400, 400);
6.   background(200);
7. }
8. 
   
9. void draw(){
10.   background (200);
11.   float m = millis();
12.   t = m % 12000; // returns 0 to 1
13.   float ypos = height/2 + -abs(sin(a) * height/2);
14.   a += PI / height;
15.   ellipse(width*t/12000, ypos, 80, 80);
16. }