thirddegreeequation.java

介绍了java的一些应用

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package 命令行解一元三次方程;
import java.math.*;
import java.io.*;
/**
 *
 * @author liuwei
 */
public class ThirdDegreeEquation {
private double a,b,c,d;
private double A,B;
private double p,q,m;//(x+m)^3+p(x+m)+q=0
private double f,g;//a*(x-x1)(x^2+f*x+g)=0
private double x1,x2,x3;
private int flag;
public ThirdDegreeEquation(double a1,double b1,double c1,double d1)
{
    a=a1;b=b1;c=c1;d=d1;
}
public void calculateRoots()
{ if(a!=0)
  {
    m=b/3/a;
    p=b*b/3/a/a-c/a;
    q=m*m*m-p*m-d/a;
    A=-1*q/2-Math.pow((Math.pow(q/2,2)+Math.pow(p/3,3)),0.5);
    B=-1*q/2+Math.pow((Math.pow(q/2,2)+Math.pow(p/3,3)),0.5); 
    double A1,B1;
    if (A<=0)
    A1=-1*Math.pow(-1*A,1.0/3);
    else A1=Math.pow(A,1.0/3);
    if (B<=0)
    B1=-1*Math.pow(-1*B,1.0/3);
    else B1=Math.pow(B,1.0/3);
    x1=A1+B1-b/3/a;
    f=b/a+x1;
    g=c/a+f*x1;
    double delta=f*f-4*g;
    if(delta>=0)
	{
	x2=(-1*f+Math.sqrt(delta))/2;
	x3=(-1*f-Math.sqrt(delta))/2;
        flag=1;
	}
    else
    {
        flag=0;
    }
  }
  else
  {
      double delta1;
    delta1=c*c-4*b*d;
    if(b==0)
    {
        flag=-1;
        x1=-1*d/c;
    }
    if(delta1>=0)
    {
      x1=(-b+(double)Math.sqrt(delta1))/(2*b);  
      x2=(-b-(double)Math.sqrt(delta1))/(2*b); 
      flag=2;
    }
    else
        flag=-2;
  }
}
    public void showRoots()
    {
        if(flag==-2)
        {
            System.out.println("No Roots");
        }
        if(flag==-1)
        {
            System.out.println("One Root:"+x1);
        }
        if(flag==0)
        {
            System.out.println("One Root:"+x1);
        }
        if(flag==1)
        {
            System.out.println("Three Roots:");
            System.out.println("X1="+x1);
            System.out.println("X2="+x2);
            System.out.println("X3="+x3);
        }
        if(flag==2)
        {
            System.out.println("Two Roots:");
            System.out.println("X1="+x1);
            System.out.println("X2="+x2);
        }
    }
   public static void main(String[] args){
        double a1=0.0,b1=0.0,c1=0.0,d1=0.0;
         try{System.out.println("Please Input a");
         BufferedReader br= new BufferedReader (new InputStreamReader(System.in));
            a1=Double.parseDouble(br.readLine());
         System.out.println("Please Input b");
        br=new BufferedReader (new InputStreamReader(System.in));
            b1=Double.parseDouble(br.readLine());
         System.out.println("Please Input c");
         br=new BufferedReader (new InputStreamReader(System.in));
            c1=Double.parseDouble(br.readLine());
         System.out.println("Please Input d");
        br=new BufferedReader (new InputStreamReader(System.in));
            d1=Double.parseDouble(br.readLine());
            }catch(IOException e){}
         ThirdDegreeEquation TDE= new ThirdDegreeEquation(a1,b1,c1,d1);
         TDE.calculateRoots();
         TDE.showRoots();
    }
}