    @Test
    public void testLearn_doubleArrArr() {

        System.out.println("learn");

        double[][] points = {
            {-41.5471709650684, 18.9187013341311},
            {40.7205435629563, 17.8623927312285},
            {49.9308397575605, 26.6606879579547},
            {-10.3370642672217, 9.00224445858628},
            {-35.0083289866438, -3.70032099791862},
            {43.9817434767359, 30.0445008138371},
            {53.9610358073703, -4.66266636863129},
            {57.7358631824272, -1.30607492157220},
            {56.1786495749734, 13.5816619077229},
            {46.8127057228977, 19.2914454308493},
            {59.0902226769002, 2.27622667625115},
            {-23.9811287149359, -19.6680495340898},
            {-31.6709879452205, -29.2396294358316},
            {-30.8738335256604, -21.3164508659988},
            {-26.4232478675269, -30.2889337565531},
            {-8.3625949282234, -27.6077828194227},
            {-43.2767141993124, 2.08695500610564},
            {-34.0665151497352, 28.1479741110468},
            {-53.6679739887328, 24.6906697729225},
            {-26.3733795110345, -33.9315334064056},
            {-27.8656506195448, -18.3462042689455},
            {-37.9026356029680, -17.9173598811782},
            {-23.8179637389194, -7.23898052191483},
            {-32.046499530676, -14.3577517651184},
            {-32.5177814790751, -35.3376717498908},
            {-34.6763890636256, -19.8778449612201},
            {-38.5490968653245, -28.9267632818002},
            {-26.8781014349665, -21.0963329790359},
            {-28.8485414670825, 17.9105069486671},
            {-35.6302869743962, -10.9302638970488},
            {69.706658204471, -19.5557970676609},
            {64.6821432344783, -18.0296263346533},
            {68.1001234975685, -23.5894780300945},
            {62.6532937426116, -10.9032392932977},
            {63.462749924443, 3.45363261991214},
            {64.5812679253935, -7.74243025724959},
            {68.873610264193, -17.9261405577515},
            {55.4373848416417, 4.83812958553159},
            {-35.5895808611236, 2.99810046659920},
            {-44.557751875965, 32.6215827953748},
            {-40.9386737894356, 22.3753055236014},
            {-31.6319135101113, 36.7099431156778},
            {-41.4105672588672, -1.45061022144205},
            {-46.1905233212182, 17.4221608481553},
            {-16.6819375141783, 66.7460385633789},
            {7.48331523512227, 13.7411283989803},
            {7.93068432504942, 33.5679481082113}
        };

        SammonMapping sammon = SammonMapping.of(swiss);
        assertEquals(0.00383, sammon.stress, 1E-5);

        double[][] coords = sammon.coordinates;
        for (int i = 0; i < points.length; i++) {
            for (int j = 0; j < points[0].length; j++) {
                assertEquals(Math.abs(points[i][j]), Math.abs(coords[i][j]), 1E-2);
            }
        }
    }