1 /*
2 * Copyright (C) 2023 Alberto Irurueta Carro (alberto@irurueta.com)
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package com.irurueta.numerical.interpolation;
17
18 import com.irurueta.algebra.Matrix;
19
20 /**
21 * Computes bicubic spline interpolation in two dimensions.
22 */
23 public class BicubicSpline2DInterpolator {
24
25 /**
26 * Length of x1v array.
27 */
28 private final int m;
29
30 /**
31 * Length of x2v array.
32 */
33 private final int n;
34
35 /**
36 * Array of x1v.
37 */
38 private final double[] x1;
39
40 /**
41 * Array of x2v.
42 */
43 private final double[] yv;
44
45 /**
46 * Array of one dimensional cubic spline interpolators.
47 */
48 private final CubicSplineInterpolator[] srp;
49
50 /**
51 * Constructor.
52 *
53 * @param x1v array of x1v.
54 * @param x2v array of x2v.
55 * @param ym matrix of tabulated function values yij.
56 */
57 public BicubicSpline2DInterpolator(final double[] x1v, final double[] x2v, final Matrix ym) {
58 m = x1v.length;
59 n = x2v.length;
60 yv = new double[m];
61 x1 = x1v;
62 srp = new CubicSplineInterpolator[m];
63
64 for (var i = 0; i < m; i++) {
65 // get i-th row of y
66 final var yi = ym.getSubmatrixAsArray(i, 0, i, ym.getColumns() - 1);
67 srp[i] = new CubicSplineInterpolator(x2v, yi);
68 }
69 }
70
71 /**
72 * Gets length of x1v array.
73 *
74 * @return length of x1v array.
75 */
76 public int getM() {
77 return m;
78 }
79
80 /**
81 * Gets length of x2v array.
82 *
83 * @return length of x2v array.
84 */
85 public int getN() {
86 return n;
87 }
88
89 /**
90 * Given values x1p an x2p, returns an interpolated value.
91 *
92 * @param x1p x1p value where interpolation is estimated.
93 * @param x2p x2p value where interpolation is estimated.
94 * @return interpolated value.
95 * @throws InterpolationException if interpolation fails.
96 */
97 public double interpolate(final double x1p, final double x2p) throws InterpolationException {
98 for (int i = 0; i < m; i++) {
99 yv[i] = srp[i].interpolate(x2p);
100 }
101
102 final var scol = new CubicSplineInterpolator(x1, yv);
103 return scol.interpolate(x1p);
104 }
105 }