generates a list , with successive elements increasing by factors of 10.
uses factors of r instead of 10.
- PowerRange effectively behaves like Range, but in "log-space".
- The arguments a and b to PowerRange need not be integers or powers of r, but must be either both positive or both negative.
- PowerRange starts from a and successively multiplies by r until the result is larger than b.
- If is not a power of r, the end point b will not be included in the list generated by PowerRange.
Introduced in 2014