import java.math.BigDecimal;

/**
 * 黃金分割法測(cè)試
 */
public class GoldenCut {
    public static final BigDecimal C=new BigDecimal("0.01");

    public static  BigDecimal end=null;

    /**
     *x^3-12x-11
     * @param x 輸入?yún)?shù)x
     * @return x^3-12x-11
     */
    public static BigDecimal ComputeFx(BigDecimal x){
        return x.pow(3).subtract(new BigDecimal("12").multiply(x)).subtract(new BigDecimal("11"))
                .setScale(10,BigDecimal.ROUND_HALF_EVEN);
    }

    /**
     * a+0.382*(b-a)
     * @param a
     * @param b
     * @return a+0.382*(b-a)
     */
    public static BigDecimal Compute382(BigDecimal a,BigDecimal b){
        return a.add(new BigDecimal("0.382").multiply(b.subtract(a)))
                .setScale(10,BigDecimal.ROUND_HALF_EVEN);
    }

    /**
     * a+0.618(b-a)
     * @param a
     * @param b
     * @return
     */
    public static BigDecimal Compute618(BigDecimal a,BigDecimal b){
        return a.add(new BigDecimal("0.618").multiply(b.subtract(a)))
                    .setScale(10,BigDecimal.ROUND_HALF_EVEN);
    }
    /**
     * a+b-x1
     * @param a
     * @param b
     * @param x1
     * @return
     */
    public static BigDecimal Subtractabx1(BigDecimal a,BigDecimal b,BigDecimal x1){
        return a.add(b).subtract(x1)
                .setScale(10,BigDecimal.ROUND_HALF_EVEN);
    }
    //判斷是否滿足精度 b-a<C？
    public static boolean OK(BigDecimal a,BigDecimal b){
        return b.subtract(a).compareTo(C) < 0;
    }
    //輸出最優(yōu)解
    public static BigDecimal Success(BigDecimal a, BigDecimal b){
        return (a.add(b)).divide(new BigDecimal("2"))
                .setScale(10,BigDecimal.ROUND_HALF_EVEN);
    }
    //修改后的黃金分割法
    public static void goldenTest1(BigDecimal a,BigDecimal b){
        System.out.println("初始化");
        BigDecimal x1=Compute382(a,b);
        BigDecimal x2=Subtractabx1(a,b,x1);
        BigDecimal f1=ComputeFx(x1);
        BigDecimal f2=ComputeFx(x2);
        System.out.println("x1="+x1);
        System.out.println("x2="+x2);
        System.out.println("f1="+f1);
        System.out.println("f2="+f2);
        System.out.println("迭代區(qū)間如下:");
        int count=0;    //迭代次數(shù)
        while(!OK(a,b)){//只要不滿足精度就一直迭代
            System.out.println("["+a+"\t,\t"+b+"]");
            count++;    //迭代次數(shù)+1
            if(f1.compareTo(f2)==1){//f1>f2
                a=x1;
                if(OK(a,b)){     //精度判斷
                    end = Success(a, b);
                    break;
                }else{
                    f1=f2;
                    x1=x2;
                    x2=Compute618(a,b);
                    f2=ComputeFx(x2);
                }
            }else{
                b=x2;
                if(OK(a,b)){
                    end = Success(a, b);
                    break;
                }else{
                    f2=f1;
                    x2=x1;
                    x1=Compute382(a,b);
                    f1=ComputeFx(x1);
                }
            }
        }
        System.out.println("迭代結(jié)束,迭代次數(shù)"+count);
    }
    public static void main(String[] args) {
        BigDecimal a=new BigDecimal("0");
        BigDecimal b=new BigDecimal("10");

        goldenTest1(a,b);
        System.out.println("最優(yōu)解為x*="+end);
        System.out.println("f(x*)="+ComputeFx(end));
    }
}