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