1 files changed, 21 insertions, 0 deletions
diff --git a/gi/posterior-regularisation/prjava/src/util/DigammaFunction.java b/gi/posterior-regularisation/prjava/src/util/DigammaFunction.java
new file mode 100644
index 00000000..ff1478ad
--- /dev/null
+++ b/gi/posterior-regularisation/prjava/src/util/DigammaFunction.java
@@ -0,0 +1,21 @@
+package util;
+
+public class DigammaFunction {
+	public static double expDigamma(double number){
+		if(number==0)return number;
+		return Math.exp(digamma(number));
+	}
+	
+	public static double digamma(double number){
+		if(number > 7){
+			return digammApprox(number-0.5);
+		}else{
+			return digamma(number+1) - 1.0/number;
+		}
+	}
+	
+	private static double digammApprox(double value){
+		return Math.log(value) + 0.04167*Math.pow(value, -2) - 0.00729*Math.pow(value, -4) 
+		+  0.00384*Math.pow(value, -6) - 0.00413*Math.pow(value, -8);
+	}
+}