java中的exp是什么??怎么用??

exp
public static double exp(double a)Returns Euler's number e raised to the power of a double value. Special cases:
If the argument is NaN, the result is NaN.
If the argument is positive infinity, then the result is positive infinity.
If the argument is negative infinity, then the result is positive zero.
The computed result must be within 1 ulp of the exact result. Results must be semi-monotonic.

Parameters:
a - the exponent to raise e to.
Returns:
the value ea, where e is the base of the natural logarithms.