* @return the random Exponential value
* @throws NotStrictlyPositiveException if {@code mean <= 0}.
*/
public double nextExponential(double mean) {
if (mean <= 0.0) {
throw new NotStrictlyPositiveException(LocalizedFormats.MEAN, mean);
}
final RandomGenerator generator = getRan();
double unif = generator.nextDouble();
while (unif == 0.0d) {
unif = generator.nextDouble();