Mega Code Archive
Linear Interpolation
<![CDATA[
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Arrays;
/**
* <p>Static methods for doing useful math</p><hr>
*
* @author : $Author: brian $
* @version : $Revision: 1.1 $
*
* <hr><p><font size="-1" color="#336699"><a href="http://www.mbari.org">
* The Monterey Bay Aquarium Research Institute (MBARI)</a> provides this
* documentation and code "as is", with no warranty, express or
* implied, of its quality or consistency. It is provided without support and
* without obligation on the part of MBARI to assist in its use, correction,
* modification, or enhancement. This information should not be published or
* distributed to third parties without specific written permission from
* MBARI.</font></p><br>
*
* <font size="-1" color="#336699">Copyright 2002 MBARI.<br>
* MBARI Proprietary Information. All rights reserved.</font><br><hr><br>
*
*/
public class Util{
public static final double[] interpLinear(double[] x, double[] y, double[] xi) throws IllegalArgumentException {
if (x.length != y.length) {
throw new IllegalArgumentException("X and Y must be the same length");
}
if (x.length == 1) {
throw new IllegalArgumentException("X must contain more than one value");
}
double[] dx = new double[x.length - 1];
double[] dy = new double[x.length - 1];
double[] slope = new double[x.length - 1];
double[] intercept = new double[x.length - 1];
// Calculate the line equation (i.e. slope and intercept) between each point
for (int i = 0; i < x.length - 1; i++) {
dx[i] = x[i + 1] - x[i];
if (dx[i] == 0) {
throw new IllegalArgumentException("X must be montotonic. A duplicate " + "x-value was found");
}
if (dx[i] < 0) {
throw new IllegalArgumentException("X must be sorted");
}
dy[i] = y[i + 1] - y[i];
slope[i] = dy[i] / dx[i];
intercept[i] = y[i] - x[i] * slope[i];
}
// Perform the interpolation here
double[] yi = new double[xi.length];
for (int i = 0; i < xi.length; i++) {
if ((xi[i] > x[x.length - 1]) || (xi[i] < x[0])) {
yi[i] = Double.NaN;
}
else {
int loc = Arrays.binarySearch(x, xi[i]);
if (loc < -1) {
loc = -loc - 2;
yi[i] = slope[loc] * xi[i] + intercept[loc];
}
else {
yi[i] = y[loc];
}
}
}
return yi;
}
public static final BigDecimal[] interpLinear(BigDecimal[] x, BigDecimal[] y, BigDecimal[] xi) {
if (x.length != y.length) {
throw new IllegalArgumentException("X and Y must be the same length");
}
if (x.length == 1) {
throw new IllegalArgumentException("X must contain more than one value");
}
BigDecimal[] dx = new BigDecimal[x.length - 1];
BigDecimal[] dy = new BigDecimal[x.length - 1];
BigDecimal[] slope = new BigDecimal[x.length - 1];
BigDecimal[] intercept = new BigDecimal[x.length - 1];
// Calculate the line equation (i.e. slope and intercept) between each point
BigInteger zero = new BigInteger("0");
BigDecimal minusOne = new BigDecimal(-1);
for (int i = 0; i < x.length - 1; i++) {
//dx[i] = x[i + 1] - x[i];
dx[i] = x[i + 1].subtract(x[i]);
if (dx[i].equals(new BigDecimal(zero, dx[i].scale()))) {
throw new IllegalArgumentException("X must be montotonic. A duplicate " + "x-value was found");
}
if (dx[i].signum() < 0) {
throw new IllegalArgumentException("X must be sorted");
}
//dy[i] = y[i + 1] - y[i];
dy[i] = y[i + 1].subtract(y[i]);
//slope[i] = dy[i] / dx[i];
slope[i] = dy[i].divide(dx[i]);
//intercept[i] = y[i] - x[i] * slope[i];
intercept[i] = x[i].multiply(slope[i]).subtract(y[i]).multiply(minusOne);
//intercept[i] = y[i].subtract(x[i]).multiply(slope[i]);
}
// Perform the interpolation here
BigDecimal[] yi = new BigDecimal[xi.length];
for (int i = 0; i < xi.length; i++) {
//if ((xi[i] > x[x.length - 1]) || (xi[i] < x[0])) {
if (xi[i].compareTo(x[x.length - 1]) > 0 || xi[i].compareTo(x[0]) < 0) {
yi[i] = null; // same as NaN
}
else {
int loc = Arrays.binarySearch(x, xi[i]);
if (loc < -1) {
loc = -loc - 2;
//yi[i] = slope[loc] * xi[i] + intercept[loc];
yi[i] = slope[loc].multiply(xi[i]).add(intercept[loc]);
}
else {
yi[i] = y[loc];
}
}
}
return yi;
}
public static final double[] interpLinear(long[] x, double[] y, long[] xi) throws IllegalArgumentException {
double[] xd = new double[x.length];
for (int i = 0; i < x.length; i++) {
xd[i] = (double) x[i];
}
double[] xid = new double[xi.length];
for (int i = 0; i < xi.length; i++) {
xid[i] = (double) xi[i];
}
return interpLinear(xd, y, xid);
}
}
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