/*
 *  call-seq:
 *     dvector.acosh   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with entry x replaced by acosh(x).
 *     
 *     a = Dvector[ 5.1, 2.2, 1.3 ]
 *     a.acosh   -> Dvector[ acosh(5.1), acosh(2.2), acosh(1.3) ]
 */ 
VALUE dvector_acosh(VALUE ary) {