/*
 *  call-seq:
 *     dvector.exp!   ->  dvector
 *  
 *  Replace each entry x of _dvector_ with exp(x).
 *     
 *     a = Dvector[ 1.1, -2.2, 5.3 ]
 *     a.exp!   -> Dvector[ exp(1.1), exp(-2.2), exp(5.3) ]
 *     a        -> Dvector[ exp(1.1), exp(-2.2), exp(5.3) ]
 */ 
VALUE dvector_exp_bang(VALUE ary) {