Math.NET 6th order polynomial fit returns infinity and NaN as parameters

Question

I'm trying to fit 100 data point using 6th order polynomial with Math.NET.

I've noticed that the fit results are very much dependant on the chosen method and so I've decided to stick with the Svd decomposition which should be the best (the difference in performance to QR or Normal is not relevant for my needs). Using Svd decomposition the results also match the fit parameters from other software (Excel).

However, I've now come across several datasets where the Svd decomposition fails (returns infinity and NaN as parameters) and QR manages to get at least sensical parameters, although they do not match the ones obtained from Excel.

Any help in understanding what is going on and fixing the issue is much appreciated!

Here's my call of the Fit.Polynomial method:

double[] PolFitCoeff = Fit.Polynomial(XValues, YValues, 6, MathNet.Numerics.LinearRegression.DirectRegressionMethod.Svd);

As a result I (correctly) get 7 elements in the PolFitCoeff array, but the first element is infinity and the rest is NaN.

XValues and YValues are arrays filtered from a larger dataset using:

// Arrays of x and y values starting from the minimum value and extending 100 nm into longer wavelengths
double[] XValues = input.Where(se => se.X >= MinUVBlueWavelenth && se.X <= MinUVBlueWavelenth + 100).Select(se => se.X).ToArray();
double[] YValues = input.Where(se => se.X >= MinUVBlueWavelenth && se.X <= MinUVBlueWavelenth + 100).Select(se => se.Y).ToArray();

Here are two examples of the data where Svd works as expected and one that is causing problems:

double[] XWorking1 = new double[] {370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470};
double[] YWorking1 = new double[] {-0.00227, 0, 0, 0.004547, 0, 0.010239, 0.007965, 0.002276, 0.007967, 0.002276, 0.002277, 0.001139, 0.00114, 0.025087, 0.01027, 0.044447, 0.157399, 0.143755, 0.142648, 0.138106, 0.135882, 0.132488, 0.133655, 0.131388, 0.133708, 0.144043, 0.166937, 0.221899, 0.334092, 0.549274, 0.926127, 1.543659, 2.490492, 3.847829, 5.696928, 8.066181, 10.973218, 14.358651, 18.197052, 22.374146, 26.828288, 31.416559, 36.102365, 40.708982, 45.16626, 49.463491, 53.530264, 57.321396, 60.836134, 64.075579, 67.014809, 69.689847, 72.089191, 74.240713, 76.18411, 77.900317, 79.423356, 80.750665, 81.92438, 82.95304, 83.853657, 84.637438, 85.315547, 85.909902, 86.418319, 86.882287, 87.275151, 87.604113, 87.904226, 88.152034, 88.380633, 88.574051, 88.744981, 88.895262, 89.031792, 89.143631, 89.240092, 89.320935, 89.402605, 89.472717, 89.527454, 89.598758, 89.644623, 89.689571, 89.720099, 89.763308, 89.801347, 89.833788, 89.859346, 89.882605, 89.906439, 89.940542, 89.942621, 89.975916, 89.994124, 90.010484, 90.058304, 90.05887, 90.057483, 90.071175, 90.089125};
double[] XWorking2 = new double[] {353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453};
double[] YWorking2 = new double[] {-2.75759524458215E-05, 8.82744009754321E-06, 5.40915272797923E-05, 3.75544539582394E-05, 1.98865362625465E-05, 1.32638308596289E-05, 1.87948519794849E-05, 4.97612015229139E-05, 5.75202786636269E-05, 2.76631906945453E-05, 6.75159658656986E-05, 8.74759856273634E-05, 4.87199929134556E-05, 8.19705725644494E-05, 0.000131830246954611, 0.000107493398021457, 0.000134093566279347, 0.000154031639650182, 0.000200584243165729, 0.00024276768462815, 0.000292696555715455, 0.000370278806637968, 0.000507548959635451, 0.000696925108804524, 0.000848325774817128, 0.00101057506480742, 0.00128081439834991, 0.00170673955890091, 0.0021450925433506, 0.00274776437474421, 0.00355134787259316, 0.00447104532303219, 0.00557349898328843, 0.00690208613991011, 0.00845707959564937, 0.010241833150862, 0.012287329319398, 0.0145353736128952, 0.0169943597652841, 0.01963496316142, 0.0225242224152523, 0.0255717274284043, 0.0287432528361527, 0.0319952150013279, 0.0352825133923142, 0.0385402961856969, 0.0417595661343778, 0.0449535755736095, 0.0479951431227533, 0.0508119761601612, 0.0535037276547127, 0.0560799171731777, 0.0584931552699401, 0.0606595397433995, 0.0626391522587842, 0.0644290601093262, 0.0660031850685414, 0.0673912219231121, 0.0686259970138369, 0.069722172672137, 0.070612231250209, 0.0714604171728813, 0.0722775522216351, 0.0729267901245575, 0.0734496512690242, 0.0739106361218835, 0.0743721929136665, 0.0747896735359017, 0.0751280940518256, 0.0754099382754536, 0.0757062989689115, 0.0759867322633067, 0.0762673100829459, 0.0765239818239271, 0.0767863419756437, 0.0770477434166765, 0.0772557202155063, 0.0774793847905566, 0.077687548982008, 0.0779263076457929, 0.0781845847083027, 0.0783634165529564, 0.0784971903404137, 0.078626804476334, 0.078803424497818, 0.0789734275919643, 0.0791337594891459, 0.0792016018575865, 0.0792757610721576, 0.0794037729989908, 0.0794377290961222, 0.0795123238226576, 0.0795988794698434, 0.0796303502161205, 0.0797138160046204, 0.0798762316963929, 0.0799921074276644, 0.0801081854005132, 0.0802696642166181, 0.0804052511542033, 0.0805767834679051};
double[] XNotWorking = new double[] {420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520};
double[] YNotWorking = new double[] {3.0244883406976, 2.83295966596341, 2.66178772393115, 2.49536986054521, 2.35247588199072, 2.19841374699224, 2.06936371068534, 1.94447612701576, 1.81831456842034, 1.69769200302452, 1.58251936763242, 1.47521907858038, 1.35135675658379, 1.25090839300155, 1.14067148661186, 1.03486600913928, 0.940885459333528, 0.841598797944357, 0.757820203011102, 0.681046307555002, 0.604403396323645, 0.540025064033112, 0.478340422261197, 0.426974657986113, 0.380669495238637, 0.344752920421447, 0.308383765576425, 0.272432523054477, 0.257553728541763, 0.234062303492469, 0.223253270206317, 0.210696726465545, 0.202538266655753, 0.203759268701798, 0.198306955613973, 0.203629801021742, 0.212560116373918, 0.220336224892702, 0.232028290678333, 0.245959346305367, 0.259218171633184, 0.2777450536022, 0.299094726645395, 0.316459804412063, 0.336837522082181, 0.361473822363433, 0.380590389468502, 0.404441363493798, 0.429219686796428, 0.45268891421585, 0.475338033132888, 0.499594235650765, 0.522422547413789, 0.547349852935894, 0.572580202632931, 0.599658563792795, 0.627115230055263, 0.656437694235189, 0.683296196948674, 0.712500622293025, 0.746534480082464, 0.777474719140242, 0.812042697632694, 0.849618263659198, 0.888244565260653, 0.928551592890494, 0.970491986073818, 1.00849410234163, 1.04626154346002, 1.09104901197512, 1.12398319460137, 1.15910129489684, 1.1959450891667, 1.227494518776, 1.2569215613004, 1.28414396566287, 1.30865735634816, 1.33254240407815, 1.35255778946778, 1.37179321554218, 1.3880305032149, 1.40317688705949, 1.41412136847739, 1.42757192488658, 1.43922979047245, 1.45122451456189, 1.46340435861582, 1.47171825187438, 1.48166055117652, 1.49385044441323, 1.50595310332654, 1.51876982551541, 1.52990961265142, 1.54201881038538, 1.55440258816695, 1.56705411648325, 1.57994676788576, 1.59261608906482, 1.60416093621065, 1.61493837998244, 1.62469252781368};