Provided a vector of per-capita growth rates, this function returns the vector of equivalent doubling times

## Arguments

- y
Vector of per-capita derivative data to calculate the equivalent doubling time of

- x_scale
Numeric to scale per-capita derivative values by

Set x_scale to the ratio of the the units of y to the desired units. E.g. if y is in per-second, but the desired doubling time is in minutes,

`x_scale = 60`

(since there are 60 seconds in 1 minute).