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