Math.Exp returns e raised to the specified power.
using System; class ExpDemo { public static void Main() { UseLnExp(9.9); } static void UseLnExp(double arg) { Console.WriteLine( "\n Math.Exp(Math.Log({0})) == {1:E16}\n" + " Math.Log(Math.Exp({0})) == {2:E16}", arg, Math.Exp(Math.Log(arg)), Math.Log(Math.Exp(arg)) ); } }