/*
 *  call-seq:
 *     dtable.atan2!(number)       ->  dtable
 *     dtable.atan2!(other)        ->  dtable
 *  
 *  When argument is a number, this operation replaces each entry x of _dtable_ by the angle whose tangent is x/_number_.
 *  When argument is a data array, this operation replaces each entry x of _dtable_ by the angle whose tangent is x divided
 *  by the corresponding entry in the _other_ data array.
 */ VALUE dtable_atan2_bang(VALUE ary, VALUE arg) {