/*
 *  call-seq:
 *     dvector.atanh   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with entry x replaced by atanh(x).
 *     
 *     a = Dvector[ 0.1, -0.2, 0.3 ]
 *     a.atanh   -> Dvector[ atanh(0.1), atanh(-0.2), atanh(0.3) ]
 */ 
VALUE dvector_atanh(VALUE ary) {