/*
 *  call-seq:
 *     dvector.cos   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with entry x replaced by cos(x).
 *     
 *     a = Dvector[ 1, -2, -3, 4 ]
 *     a.cos   -> Dvector[ cos(1), cos(-2), cos(-3), cos(4) ]
 */ 
VALUE dvector_cos(VALUE ary) {