gmedian fails on duplicate entries

[drewhk]

I have an issue where part of the 2D data I input might contain duplicates. In these cases the gmedian method returns NaN results. A simple reproducer:

        let d1 = vec![700000.0, 700000.0];
        let d2 = vec![700000.0, 700000.0];
        let d3 = vec![700001.0, 700000.0];
        let result = [d1, d2].gmedian(0.000_000_1);
        assert!(!result[0].is_nan());
        assert!(!result[1].is_nan());

If you add d3 to the data the above test will pass. As far as I understand a geometric median should not be affected by duplicate data, so this is likely a bug somewhere.