summaryrefslogtreecommitdiff
path: root/gi/posterior-regularisation/prjava/src/util/LogSummer.java
diff options
context:
space:
mode:
Diffstat (limited to 'gi/posterior-regularisation/prjava/src/util/LogSummer.java')
-rw-r--r--gi/posterior-regularisation/prjava/src/util/LogSummer.java86
1 files changed, 0 insertions, 86 deletions
diff --git a/gi/posterior-regularisation/prjava/src/util/LogSummer.java b/gi/posterior-regularisation/prjava/src/util/LogSummer.java
deleted file mode 100644
index 117393b9..00000000
--- a/gi/posterior-regularisation/prjava/src/util/LogSummer.java
+++ /dev/null
@@ -1,86 +0,0 @@
-package util;
-
-import java.lang.Math;
-
-/*
- * Math tool for computing logs of sums, when the terms of the sum are already in log form.
- * (Useful if the terms of the sum are very small numbers.)
- */
-public class LogSummer {
-
- private LogSummer() {
- }
-
- /**
- * Given log(a) and log(b), computes log(a + b).
- *
- * @param loga log of first sum term
- * @param logb log of second sum term
- * @return log(sum), where sum = a + b
- */
- public static double sum(double loga, double logb) {
- assert(!Double.isNaN(loga));
- assert(!Double.isNaN(logb));
-
- if(Double.isInfinite(loga))
- return logb;
- if(Double.isInfinite(logb))
- return loga;
-
- double maxLog;
- double difference;
- if(loga > logb) {
- difference = logb - loga;
- maxLog = loga;
- }
- else {
- difference = loga - logb;
- maxLog = logb;
- }
-
- return Math.log1p(Math.exp(difference)) + maxLog;
- }
-
- /**
- * Computes log(exp(array[index]) + b), and
- * modifies array[index] to contain this new value.
- *
- * @param array array to modify
- * @param index index at which to modify
- * @param logb log of the second sum term
- */
- public static void sum(double[] array, int index, double logb) {
- array[index] = sum(array[index], logb);
- }
-
- /**
- * Computes log(a + b + c + ...) from log(a), log(b), log(c), ...
- * by recursively splitting the input and delegating to the sum method.
- *
- * @param terms an array containing the log of all the terms for the sum
- * @return log(sum), where sum = exp(terms[0]) + exp(terms[1]) + ...
- */
- public static double sumAll(double... terms) {
- return sumAllHelper(terms, 0, terms.length);
- }
-
- /**
- * Computes log(a_0 + a_1 + ...) from a_0 = exp(terms[begin]),
- * a_1 = exp(terms[begin + 1]), ..., a_{end - 1 - begin} = exp(terms[end - 1]).
- *
- * @param terms an array containing the log of all the terms for the sum,
- * and possibly some other terms that will not go into the sum
- * @return log of the sum of the elements in the [begin, end) region of the terms array
- */
- private static double sumAllHelper(final double[] terms, final int begin, final int end) {
- int length = end - begin;
- switch(length) {
- case 0: return Double.NEGATIVE_INFINITY;
- case 1: return terms[begin];
- default:
- int midIndex = begin + length/2;
- return sum(sumAllHelper(terms, begin, midIndex), sumAllHelper(terms, midIndex, end));
- }
- }
-
-} \ No newline at end of file