package com.gunshi.project.xyt.util;

import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;

/**
 * @author cxw
 * @description
 * @classname BigdecimalUtil.java
 * @create 2024-11-06, 星期三, 10:33:41
 */
public class BigdecimalUtil {


    /**
     * @description: 小数指数计算
     * @param base 底数
     * @param exponent 指数
     * @return: java.math.BigDecimal
     * @auther: cxw
     * @date: 2024-11-06, 周三, 10:34:47
     */
    public static BigDecimal bigDecimalExponentiation(BigDecimal base, double exponent) {
        BigDecimal result = BigDecimal.valueOf(Math.pow(base.doubleValue(), exponent)).round(new MathContext(10, RoundingMode.HALF_UP));
        return result;
    }


    /**
     * @description: 计算x的伽马函数
     * @param x
     * @return: java.math.BigDecimal
     * @auther: cxw
     * @date: 2024-11-06, 周三, 11:31:24
     */
    public static BigDecimal bigDecimalGamma(BigDecimal x) {
        BigDecimal result = BigDecimal.valueOf(gamma(x.doubleValue()));
        return result.setScale(x.scale(), RoundingMode.HALF_UP);
    }
    public static double gamma(double x) {
        return Math.exp(logGamma(x));
    }
    public static double logGamma(double x) {
        double tmp = (x - 0.5) * Math.log(x + 4.5) - (x + 4.5);
        double ser = 1.0 + 76.18009173 / (x + 0) - 86.50532033 / (x + 1)
                + 24.01409822 / (x + 2) - 1.231739516 / (x + 3)
                + 0.00120858003 / (x + 4) - 0.00000536382 / (x + 5);
        return tmp + Math.log(ser * Math.sqrt(2 * Math.PI));
    }
}