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這篇文章將為大家詳細(xì)講解有關(guān)Apache Commons Math3探索之多項(xiàng)式曲線擬合的示例分析,小編覺(jué)得挺實(shí)用的,因此分享給大家做個(gè)參考,希望大家閱讀完這篇文章后可以有所收獲。
具體如下。
多項(xiàng)式曲線擬合:org.apache.commons.math4.fitting.PolynomialCurveFitter類。
用法示例代碼:
// ... 創(chuàng)建并初始化輸入數(shù)據(jù): double[] x = new double[...]; double[] y = new double[...]; 將原始的x-y數(shù)據(jù)序列合成帶權(quán)重的觀察點(diǎn)數(shù)據(jù)序列: WeightedObservedPoints points = new WeightedObservedPoints(); // 將x-y數(shù)據(jù)元素調(diào)用points.add(x[i], y[i])加入到觀察點(diǎn)序列中 // ... PolynomialCurveFitter fitter = PolynomialCurveFitter.create(degree); // degree 指定多項(xiàng)式階數(shù) double[] result = fitter.fit(points.toList()); // 曲線擬合,結(jié)果保存于雙精度數(shù)組中,由常數(shù)項(xiàng)至最高次冪系數(shù)排列
首先要準(zhǔn)備好待擬合的曲線數(shù)據(jù)x和y,這是兩個(gè)double數(shù)組,然后把這兩個(gè)數(shù)組合并到WeightedObservedPoints對(duì)象實(shí)例中,可以調(diào)用WeightedObservedPoints.add(x[i], y[i])將x和y序列中的數(shù)據(jù)逐個(gè)添加到觀察點(diǎn)序列對(duì)象中。隨后創(chuàng)建PolynomialCurveFitter對(duì)象,創(chuàng)建時(shí)要指定擬合多項(xiàng)式的階數(shù),注意階數(shù)要選擇適當(dāng),不是越高越好,否則擬合誤差會(huì)很大。最后調(diào)用PolynomialCurveFitter的fit方法即可完成多項(xiàng)式曲線擬合,fit方法的參數(shù)通過(guò)WeightedObservedPoints.toList()獲得。擬合結(jié)果通過(guò)一個(gè)double數(shù)組返回,按元素順序依次是常數(shù)項(xiàng)、一次項(xiàng)、二次項(xiàng)、……。
完整的演示代碼如下:
interface TestCase { public Object run(List<Object> params) throws Exception; public List<Object> getParams(); public void printResult(Object result); } class CalcCurveFitting implements TestCase { public CalcCurveFitting() { System.out.print("本算例用于計(jì)算多項(xiàng)式曲線擬合。正在初始化 計(jì)算數(shù)據(jù)(" + arrayLength + "點(diǎn), " + degree + "階)... ..."); inputDataX = new double[arrayLength]; // inputDataX = new double[] {1, 2, 3, 4, 5, 6, 7}; inputDataY = new double[inputDataX.length]; double[] factor = new double[degree + 1]; // N階多項(xiàng)式會(huì)有N+1個(gè)系數(shù),其中之一為常數(shù)項(xiàng) for(int index = 0; index < factor.length; index ++) { factor[index] = index + 1; } for(int index = 0; index < inputDataY.length; index ++) { inputDataX[index] = index * 0.00001; inputDataY[index] = calcPoly(inputDataX[index], factor); // y = sum(x[n) * fact[n]) // System.out.print(inputDataY[index] + ", "); } points = new WeightedObservedPoints(); for(int index = 0; index < inputDataX.length; index ++) { points.add(inputDataX[index], inputDataY[index]); } System.out.println("初始化完成"); } @Override public List<Object> getParams() { List<Object> params = new ArrayList<Object>(); params.add(points); return params; } @Override public Object run(List<Object> params) throws Exception { PolynomialCurveFitter fitter = PolynomialCurveFitter.create(degree); WeightedObservedPoints points = (WeightedObservedPoints)params.get(0); double[] result = fitter.fit(points.toList()); return result; } @Override public void printResult(Object result) { for(double data : (double[])result) { System.out.println(data); } } private double calcPoly(double x, double[] factor) { double y = 0; for(int deg = 0; deg < factor.length; deg ++) { y += Math.pow(x, deg) * factor[deg]; } return y; } private double[] inputDataX = null; private double[] inputDataY = null; private WeightedObservedPoints points = null; private final int arrayLength = 200000; private final int degree = 5; // 階數(shù) } public class TimeCostCalculator { public TimeCostCalculator() { } /** * 計(jì)算指定對(duì)象的運(yùn)行時(shí)間開(kāi)銷(xiāo)。 * * @param testCase 指定被測(cè)對(duì)象。 * @return 返回sub.run的時(shí)間開(kāi)銷(xiāo),單位為s。 * @throws Exception */ public double calcTimeCost(TestCase testCase) throws Exception { List<Object> params = testCase.getParams(); long startTime = System.nanoTime(); Object result = testCase.run(params); long stopTime = System.nanoTime(); testCase.printResult(result); System.out.println("start: " + startTime + " / stop: " + stopTime); double timeCost = (stopTime - startTime) * 1.0e-9; return timeCost; } public static void main(String[] args) throws Exception { TimeCostCalculator tcc = new TimeCostCalculator(); double timeCost; System.out.println("--------------------------------------------------------------------------"); timeCost = tcc.calcTimeCost(new CalcCurveFitting()); System.out.println("time cost is: " + timeCost + "s"); System.out.println("--------------------------------------------------------------------------"); } }
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