weifen.java

计算方法课

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.lang.*;
public class weifen extends Applet implements ActionListener{
  Button A, B, C,D;
  boolean choosea, chooseb, choosec,choosed;
  double x0,y0,h;
  public void init() {
    A = new Button("直接欧拉法");
    B = new Button("改进欧拉法");
    C = new Button("四阶龙格库塔法");
    D = new Button("y(x)=1/(2*exp(x)-x-1)");
    add(D);add(A);add(B);add(C);
    A.addActionListener(this);B.addActionListener(this);
    C.addActionListener(this);D.addActionListener(this);
    x0=0;y0=1;h=0.01;
  }
  public double fdao(double x,double y){
    return(-y-x*y*y);
  }
  public double yzq(double x){
    return(1/(2*Math.exp(x)-x-1));
  }

  public void actionPerformed(ActionEvent ae) {
    String str = ae.getActionCommand();
    if (str.equals("y(x)=1/(2*exp(x)-x-1)")) {
      choosea = true;//chooseb=false;choosec=false;choosed=false;
      repaint();
    }
    if (str.equals("直接欧拉法")) {
      chooseb = true;//choosea = false;choosec=false;choosed=false;
      repaint();
    }
    if (str.equals("改进欧拉法")) {
      choosec = true;//choosea = false;chooseb=false;choosed=false;
      repaint();
    }
    if (str.equals("四阶龙格库塔法")) {
      choosed = true;//choosea = false;chooseb=false;choosec=false;
      repaint();
    }
  }

  public void paint(Graphics g) { //绘图
    g.drawLine(50, 350, 50, 30);
    g.drawLine(50, 350, 500, 350);
    g.drawLine(50, 30, 54, 39);
    g.drawLine(50, 30, 46, 39);
    g.drawLine(500, 350, 495, 345);
    g.drawLine(500, 350, 495, 355);
    g.drawString("x", 505, 360);
    g.drawString("y", 40, 32);
    g.drawString("0", 40, 355);
    g.drawLine(50,280,55,280);g.drawString("0.25", 20, 285);
    g.drawLine(50,210,55,210);g.drawString("0.5", 23, 215);
    g.drawLine(50,140,55,140);g.drawString("0.75", 20, 145);
    g.drawLine(50,70,55,70);g.drawString("1", 40, 75);
    for(int i=1;i<5;i++)
        g.drawLine(50+i*100,350,50+i*100,345);//比例为1：100
    g.drawString("1",148,365);g.drawString("2",248,365);
    g.drawString("3",348,365);g.drawString("4",448,365);

    g.drawLine(400, 40, 423, 40);g.drawString("原微分曲线", 425, 45);
    g.setColor(Color.blue);g.drawLine(400, 60, 423, 60);
    g.drawString("直接欧拉法", 425, 65);
    g.setColor(Color.red);g.drawLine(400, 80, 423, 80);
    g.drawString("改进欧拉法", 425, 85);
    g.setColor(Color.green);g.drawLine(400, 100, 423, 100);
    g.drawString("四阶龙格库塔法", 425, 105);
    if (choosea) {
      g.setColor(Color.black);
      int m=50,n=70;
      double a=0.1,j;
      for(int k=50;k<450;k++){
        j=yzq(a)*280;
        /*try{
          Thread.sleep(5);//延迟
        }catch(InterruptedException e){}*/
        g.drawLine(m,n,k,350-(int)j);
        m=k;n=350-(int)j;
        a+=0.01;
      }
    }
    if (chooseb) {
      g.setColor(Color.blue);
      double x00=x0,y00=y0,j,x1,y1;
      int m=50,n=70;
      for(int k=50;k<=450;k++){
        x1=x00+h;
        y1=y00+h*fdao(x00,y00);
        j=y1*280;
        /*try{
          Thread.sleep(5);//延迟
        }catch(InterruptedException e){}*/
        g.drawLine(m,n,k,350-(int)j);
        m=k;n=350-(int)j;
        x00=x1;y00=y1;
      }
    }
    if(choosec){
      g.setColor(Color.red);
      double x00=x0,y00=y0,yp,yc,j,x1,y1;
      int m=50,n=70;
      for(int k=50;k<=450;k++){
        x1=x00+h;
        yp=y00+h*fdao(x00,y00);
        yc=y00+h*fdao(x1,yp);
        y1=(yp+yc)/2;
        j=y1*280;
       /*try{
          Thread.sleep(5);//延迟
        }catch(InterruptedException e){}*/
       g.drawLine(m,n,k,350-(int)j);
        m=k;n=350-(int)j;
        x00=x1;y00=y1;
      }
    }
    if(choosed){
      g.setColor(Color.green);
      double x00=x0,y00=y0,k1,k2,k3,k4,j,x1,y1;
      int m=50,n=70;
      for(int k=50;k<=450;k++){
        x1=x00+h;
        k1=fdao(x00,y00);
        k2=fdao(x00+h/2,y00+k1*h/2);
        k3=fdao(x00+h/2,y00+k2*h/2);
        k4=fdao(x1,y00+h*k3);
        y1=y00+(k1+2*k2+2*k3+k4)*h/6;
        j=y1*280;
        /*try{
          Thread.sleep(5);//延迟
        }catch(InterruptedException e){}*/
        g.drawLine(m,n,k,350-(int)j);
        m=k;n=350-(int)j;
        x00=x1;y00=y1;
      }
    }
  }
}