Covid-19 Case Numbers - Equatio

The trend of the sum of all positively tested people over the days is comparable to the penetration of long rods as a function of increasing impact velocity in armored steel:

The first part of the curve is exponential. After a point of inflection, the curve flattens and approaches a limit value asymptotically.

y = cumulative total of cases
x = days after first case
The parameters a, b and n can be fitted from the sums of all positively tested people over the days. The condition is that the point of inflection has been passed.

The first derivative of the general equation yields in case of covid-19 to the sum of the daily cases and in case of long rods to the growth rate of the penetration depth.

The fit values a, b and n can be used to predict the sum of all positively tested people over the days as well as the daily cases.

Numerical examples are given in Case Numbers in Switzerland.