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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);
}
}
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