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