/*
 *  call-seq:
 *     dvector.dot(other)   ->  number
 *  
 *  Returns the sum of the products of entries in _dvector_ and _other_. Returns 0.0 if
 *  _dvector_ is empty.  The vectors must be the same length.
 *     
 *     a = Dvector[ 1, 2, 3, 4 ]
 *     b = Dvector[ 1, -3, 3, 0 ]
 *     a.dot(b)        -> 4
 *     Dvector[].dot(b)   -> 0
 */ 
VALUE dvector_dot(VALUE ary1, VALUE ary2) {