function compute_growth(arr, i, prop, off = 7) {
const avg = 7;
const off2 = Math.round(off/2);
const x0 = compute_avg(arr,prop,i-off2,avg);
const x1 = compute_avg(arr,prop,i+off-off2,avg);
return x0 ? Math.pow(x1/x0, infection_interval/off) : null;
}