moremath.java

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package ir.utilities;

import java.util.*;
import java.io.*;

/** A place to put some additional math functions 
 *
 * @author Ray Mooney
*/

public class MoreMath
{
    /** Round a double to the given number of decimalPlaces */
    public static double roundTo(double num, int decimalPlaces) {
	double factor = Math.pow(10, decimalPlaces);
	return Math.round(num * factor) / factor;
    }


    /** Return logarithm of a given base */
    public static double log(double x, double base) {
	return Math.log(x) / Math.log(base);
    }

    public static double log(int x, int base) {
	return log ((double)x, (double)base);
    }

    public static double log(double x, int base) {
	return log(x, (double)base);
    }

    public static double log(int x, double base) {
	return log((double)x, base);
    }
	
    /** Add two vectors and return the vector sum */
    public static double[] addVectors(double[] x, double[] y) {
	if (x.length != y.length) {
	    System.out.println("\nTried to add vectors of unequal length");
	    System.exit(1);
	}
	double[] sum = new double[x.length];
	for(int i = 0; i < x.length; i++) 
	    sum[i] = x[i] + y[i];
	return sum;
    }

    /** Divide a vector by a scalar and return the resulting vector */
    public static double[] vectorDivide(double[] x, double c) {
	double[] result = new double[x.length];
	for(int i = 0; i < x.length; i++) 
	    result[i] = x[i]/c;
	return result;
    }

    /** Average all of the vectors in a list of vectors and return
     * the average vector.
     */
    public static double[] averageVectors(ArrayList list) {
	double[] result = new double[((double[])list.get(0)).length];
	for(int i = 0; i < list.size(); i++) 
	    result = addVectors(result, (double[])list.get(i));
	return vectorDivide(result, list.size());
    }

    /** Print a vector in the form [x,y,...z] to standard out */
    public static void printVector(double[] x) {
	printVector(x, System.out);
    }

    /** Print a vector in the form [x,y,...z] to the print stream */
    public static void printVector(double[] x, PrintStream out) {
	out.print("[");
	for(int i = 0; i < x.length; i++) {
  	    out.print(x[i]);
  	    if (i != (x.length - 1))
  		out.print(", ");
  	}
	out.print("]");
    }

    public static double vectorLength(double[] x) {
	double sumSquares = 0;
	for(int i = 0; i < x.length; i++) {
	    sumSquares = sumSquares + Math.pow(x[i], 2);
	}
	return Math.sqrt(sumSquares);
    }

    public static double vectorOneNorm(double[] x) {
	double sum = 0;
	for(int i = 0; i < x.length; i++) {
	    sum = sum + Math.abs(x[i]);
	}
	return sum;
    }


}