/*
 *  call-seq:
 *     dvector.collect {|x| block }  -> a_dvector
 *     dvector.map     {|x| block }  -> a_dvector
 *  
 *  Invokes <i>block</i> once for each element of _dvector_.
 *  Returns a new vector holding the values returned by _block_.
 *  Note that for numeric operations on long vectors, it is more efficient to
 *  apply the operator directly to the vector rather than using map or collect.
 *     
 *     a = Dvector[ 1, 2, 3, 4 ]
 *     a.map {|x| x**2 + 1 }      -> Dvector[ 2, 5, 10, 17 ]
 *    A better way:
 *     a = Dvector[ 1, 2, 3, 4 ]
 *     a**2 + 1                   -> Dvector[ 2, 5, 10, 17 ]
 */ VALUE dvector_collect(VALUE ary) {