@Override public PiecewisePolynomialResult interpolate(final double[] xValues, final double[] yValues) { ArgumentChecker.notNull(xValues, "xValues"); ArgumentChecker.notNull(yValues, "yValues"); ArgumentChecker.isTrue( xValues.length == yValues.length | xValues.length + 2 == yValues.length, "(xValues length = yValues length) or (xValues length + 2 = yValues length)"); ArgumentChecker.isTrue(xValues.length > 2, "Data points should be more than 2"); final int nDataPts = xValues.length; final int yValuesLen = yValues.length; for (int i = 0; i < nDataPts; ++i) { ArgumentChecker.isFalse(Double.isNaN(xValues[i]), "xValues containing NaN"); ArgumentChecker.isFalse(Double.isInfinite(xValues[i]), "xValues containing Infinity"); } for (int i = 0; i < yValuesLen; ++i) { ArgumentChecker.isFalse(Double.isNaN(yValues[i]), "yValues containing NaN"); ArgumentChecker.isFalse(Double.isInfinite(yValues[i]), "yValues containing Infinity"); } for (int i = 0; i < nDataPts - 1; ++i) { for (int j = i + 1; j < nDataPts; ++j) { ArgumentChecker.isFalse(xValues[i] == xValues[j], "xValues should be distinct"); } } double[] xValuesSrt = Arrays.copyOf(xValues, nDataPts); double[] yValuesSrt = new double[nDataPts]; if (nDataPts == yValuesLen) { yValuesSrt = Arrays.copyOf(yValues, nDataPts); } else { yValuesSrt = Arrays.copyOfRange(yValues, 1, nDataPts + 1); } ParallelArrayBinarySort.parallelBinarySort(xValuesSrt, yValuesSrt); final double[] intervals = _solver.intervalsCalculator(xValuesSrt); final double[] slopes = _solver.slopesCalculator(yValuesSrt, intervals); final PiecewisePolynomialResult result = _method.interpolate(xValues, yValues); ArgumentChecker.isTrue(result.getOrder() >= 3, "Primary interpolant should be degree >= 2"); final double[] initialFirst = _function.differentiate(result, xValuesSrt).getData()[0]; final double[] initialSecond = _function.differentiateTwice(result, xValuesSrt).getData()[0]; double[] first = firstDerivativeCalculator(yValuesSrt, intervals, slopes, initialFirst); boolean modFirst = false; int k; double[] aValues = aValuesCalculator(slopes, first); double[] bValues = bValuesCalculator(slopes, first); double[][] intervalsA = getIntervalsA(intervals, slopes, first, bValues); double[][] intervalsB = getIntervalsB(intervals, slopes, first, aValues); while (modFirst == false) { k = 0; for (int i = 0; i < nDataPts - 2; ++i) { if (first[i + 1] > 0.) { if (intervalsA[i + 1][1] + Math.abs(intervalsA[i + 1][1]) * ERROR < intervalsB[i][0] - Math.abs(intervalsB[i][0]) * ERROR | intervalsA[i + 1][0] - Math.abs(intervalsA[i + 1][0]) * ERROR > intervalsB[i][1] + Math.abs(intervalsB[i][1]) * ERROR) { ++k; first[i + 1] = firstDerivativesRecalculator(intervals, slopes, aValues, bValues, i + 1); } } } if (k == 0) { modFirst = true; } aValues = aValuesCalculator(slopes, first); bValues = bValuesCalculator(slopes, first); intervalsA = getIntervalsA(intervals, slopes, first, bValues); intervalsB = getIntervalsB(intervals, slopes, first, aValues); } final double[] second = secondDerivativeCalculator(initialSecond, intervalsA, intervalsB); final double[][] coefs = _solver.solve(yValuesSrt, intervals, slopes, first, second); for (int i = 0; i < nDataPts - 1; ++i) { for (int j = 0; j < 6; ++j) { ArgumentChecker.isFalse(Double.isNaN(coefs[i][j]), "Too large input"); ArgumentChecker.isFalse(Double.isInfinite(coefs[i][j]), "Too large input"); } } return new PiecewisePolynomialResult( new DoubleMatrix1D(xValuesSrt), new DoubleMatrix2D(coefs), 6, 1); }