/*
 *  call-seq:
 *     dvector.exp   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with each entry x replaced by exp(x).
 *     
 *     a = Dvector[ 1.1, -2.2, 5.3 ]
 *     a.exp   -> Dvector[ exp(1.1), exp(-2.2), exp(5.3) ]
 */ 
VALUE dvector_exp(VALUE ary) {