1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.nabla;
18
19 import java.util.Random;
20
21 public class Polynomial implements ReferenceFunction {
22
23 /** Build a random polynomial.
24 * @param random random generator to use
25 * @param degree
26 * @return a random polynomial
27 */
28 public static Polynomial randomPolynomial(Random random, int degree) {
29 double[] coeffs = new double[degree+1];
30 for (int i = 0; i < coeffs.length; ++i) {
31 coeffs[i] = random.nextDouble();
32 }
33 return new Polynomial(coeffs);
34 }
35
36 /** Build a polynomial from its coefficients.
37 * @param coeffs coefficients array in <em>decreasing degree</em> order
38 */
39 public Polynomial(double[] coeffs) {
40 this.coeffs = coeffs;
41 }
42
43 public void addToSelf(Polynomial other) {
44 double[] newCoeffs = new double[Math.max(coeffs.length, other.coeffs.length)];
45 System.arraycopy(coeffs, 0, newCoeffs, 0, coeffs.length);
46 for (int i = 0; i < other.coeffs.length; ++i) {
47 newCoeffs[i] += other.coeffs[i];
48 }
49 coeffs = newCoeffs;
50 }
51
52 public double f(double t) {
53 double y = 0;
54 for (int i = 0; i < coeffs.length; ++i) {
55 y = y * t + coeffs[i];
56 }
57 return y;
58 }
59
60 public double fPrime(double t) {
61 double d = 0;
62 for (int i = 0; i < coeffs.length - 1; ++i) {
63 d = d * t + (coeffs.length - 1 - i) * coeffs[i];
64 }
65 return d;
66 }
67
68 private double[] coeffs;
69
70 }