edu.cmu.tetrad.util.MathUtils Maven / Gradle / Ivy
///////////////////////////////////////////////////////////////////////////////
// For information as to what this class does, see the Javadoc, below. //
// Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, //
// 2007, 2008, 2009, 2010, 2014, 2015, 2022 by Peter Spirtes, Richard //
// Scheines, Joseph Ramsey, and Clark Glymour. //
// //
// This program is free software; you can redistribute it and/or modify //
// it under the terms of the GNU General Public License as published by //
// the Free Software Foundation; either version 2 of the License, or //
// (at your option) any later version. //
// //
// This program is distributed in the hope that it will be useful, //
// but WITHOUT ANY WARRANTY; without even the implied warranty of //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
// GNU General Public License for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program; if not, write to the Free Software //
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA //
///////////////////////////////////////////////////////////////////////////////
package edu.cmu.tetrad.util;
import org.apache.commons.math3.util.FastMath;
/**
* Some extra mathematical functions not contained in org.apache.commons.math3.util.FastMath.
*
* @author josephramsey
*/
public class MathUtils {
/**
* @param x a double value.
* @return the logistic function of x = 1 / (1 + exp(-x)).
*/
public static double logistic(double x) {
return 1. / (1. + FastMath.exp(-x));
}
public static int factorial(int n) {
int i = 1;
for (int j = 1; j <= n; j++) {
i *= j;
}
return i;
}
public static double logFactorial(int n) {
double i = 0;
for (int j = 1; j <= n; j++) {
i += FastMath.log(j);
}
return i;
}
public static int choose(int a, int b) {
if (a == 0 && b == 0) {
return 1;
} else if (a == 0 && b > 0) {
return (int) FastMath.round(FastMath.exp(1 - (MathUtils.logFactorial(b) + MathUtils.logFactorial(-b))));
} else if (a > 0 && b == 0) {
return (int) FastMath.round(FastMath.exp(MathUtils.logFactorial(a) - (1 + MathUtils.logFactorial(a))));
} else if (a > 0 && b > 0) {
return (int) FastMath.round(FastMath.exp(MathUtils.logFactorial(a) - (MathUtils.logFactorial(b) + MathUtils.logFactorial(a - b))));
} else {
throw new IllegalArgumentException();
}
}
public static double logChoose(int a, int b) {
return MathUtils.logFactorial(a) - (MathUtils.logFactorial(b) + MathUtils.logFactorial(a - b));
}
}