my $X = pdl([1, -4, 7],
             [-2, 3, 3]);
my $Y = pdl([8, -9, -6,  5],
            [1, -3, -4,  7],
            [2,  8, -8, -3],
            [1,  2, -5, -1]);
my $XY =pdl([  8,  -9, -6,   5, -32,  36,  24, -20, 56, -63, -42,  35],
            [  1,  -3, -4,   7,  -4,  12,  16, -28,  7, -21, -28,  49],
            [  2,   8, -8,  -3,  -8, -32,  32,  12, 14,  56, -56, -21],
            [  1,   2, -5,  -1,  -4,  -8,  20,   4,  7,  14, -35,  -7],
            [-16,  18, 12, -10,  24, -27, -18,  15, 24, -27, -18,  15],
            [ -2,   6,  8, -14,   3,  -9, -12,  21,  3,  -9, -12,  21],
            [ -4, -16, 16,   6,   6,  24, -24,  -9,  6,  24, -24,  -9],
            [ -2,  -4, 10,   2,   3,   6, -15,  -3,  3,   6, -15,  -3]);