NDGRID produces ndgrid-style coordinate arrays

 CALL: [X1, X2, ...] = ndgrid (X)

    produces ndgrid-style coordinate arrays X1, X2, ... Xd based on the
    @stk_factorialdesign object X (where d is the number of columns of
    X). This is equivalent to

       [X1, ..., Xd] = ndgrid (X.levels{1}, ..., X.levels{d});

 See also: ndgrid