/*
 *  call-seq:
 *     dtable.atan2(number)       ->  a_dtable
 *     dtable.atan2(other)        ->  a_dtable
 *  
 *  When argument is a number, this operation returns a copy of _dtable_ with each entry x replaced by the angle whose tangent is x/_number_.
 *  When argument is a data array, this operation returns a copy of _dtable_ with each entry x replaced
 *  by the angle whose tangent is x divided by the corresponding entry in the _other_ data array.
 */ VALUE dtable_atan2(VALUE ary, VALUE arg) {