get more decimals?!?! please help!

[michcio]

hello I wonder if there is a way to easy store a huge amount decimals. I have done a program that returns PI with many decimals that are right...But double can only store up to 14 decimals...how could I show my PI(System.out.println:D) ?? please help!!!

here is my short code

    public static void main(String[] args) {
double summa = 0;
for(double i=0; i<100; i++)
            
summa += Math.pow((-1),i)/(2*i+1) * (4/(Math.pow(5,(2*i+1)))-(1/Math.pow(239, (2*i+1))));
summa *= 4;
System.out.println(summa);
        
                
    }

}

it's a really short program that only add 100 of elemnts and then I got 14 deciomals right...but please help how do I do so I can see more then 14 decimals??????:(

[rjuyal]

how about BigDecimal!!! :)

[michcio]

ah nice I didn't know there was a special class for this :D...can BigDecimal have as many Decimals I want?...can you explain a bit how I should use it :o

[rjuyal]

Just like you working with double

But don't use +, - , *, / , instead use its owb methods:


See the link, This might be helpful for you:

http://java.sun.com/j2se/1.5.0/docs/...igDecimal.html

[michcio]

wow nice now I can finally write my PI :D ty very much :D

[rjuyal]

How about closing the thread as Solved :D

[michcio]

yeah how do I do that?

[michcio]

ok so I have worked a lot with BigDecimals now but I find them very slow...I have found a easy method to take sqrt of BigDeciamals (I need this method while describing decimals of PI) and a fast way to describe PI's decimals...though when I set the MathContext to 10^6 decimals and my computer is on for 24 h the program hasn't done the first for-loop yet:O look at my code:

public static void main(String[] args) throws IOException{
       [COLOR="DarkOrange"][SIZE="4"][B]//reading PI's decimals so I can compare them with thoes I count[/B][/SIZE]
       BufferedReader br = new BufferedReader
                           (new FileReader("PI1.txt"));
        String PI = "";
        int k = 0;
        while(true){
            String fil = br.readLine();
            if(fil==null)
                break;
            PI += fil;
        }
        br.close();[/COLOR]
       [COLOR="Green"] [SIZE="4"][B]//describing MathContext and some variables[/B][/SIZE]
        MathContext mode = new MathContext(1000000);
        BigDecimal a0 = new BigDecimal(1);
        BigDecimal b0 = new BigDecimal(1).divide(sqrt(new BigDecimal(2),mode),mode);
        BigDecimal t0 = new BigDecimal(0.25);
        BigDecimal p0 = a0;
        int iterationer = 16;
        boolean fortsätt = true;
        int totalt = 0;[/COLOR]
        while(fortsätt){
       [COLOR="Red"] 
        [SIZE="4"][B]//the intersesting for-loop [/B][/SIZE]
        for(int i=1; i<=iterationer; i++){
            BigDecimal a1 = (a0.add(b0,mode)).divide(new BigDecimal(2),mode);
            BigDecimal b1 = sqrt(a0.multiply(b0,mode),mode);
            BigDecimal t1 = t0.subtract(p0.multiply(a0.subtract(a1).pow(2),mode),mode);
            BigDecimal p1 = p0.multiply(new BigDecimal(2),mode);
            a0 = a1;
            b0 = b1;
            t0 = t1;
            p0 = p1;
            System.out.println((i+totalt) + " varv av " + (iterationer+totalt));
        }[/COLOR]
        BigDecimal summa = a0.add(b0,mode).pow(2,mode).divide(t0.multiply(new BigDecimal(4),mode),mode);
        System.out.println("Antal rätt decimaler = " + (antalsamma((summa + ""),PI)-2));
        if(JOptionPane.showConfirmDialog(null,"Fortsätta?","Pi",JOptionPane.YES_NO_OPTION)==JOptionPane.YES_OPTION){
            fortsätt = true;
            totalt += iterationer;
            iterationer = Integer.parseInt(JOptionPane.showInputDialog("Hur många iterationer till?") );
   }
        else
            fortsätt = false;
  } 
}
[COLOR="Silver"] 
[SIZE="4"][B]   // some of my decimals to the left, number of loops, to the right the correct                    
   //number of decimals[/B][/SIZE]
   //varv        rätt decimaler
    // 9              1 391
    // 10             2 787
    // 11             5 581
    // 12             11 170
    // 13             22 347
    // 14             44 700
    // 15             89 409
    // 16             178 824 
    // 17             >200 000[/COLOR]
    
   [COLOR="Teal"][SIZE="4"][B]//a method to compare my PI with the one I have read in the beginning of 
   //this program[/B][/SIZE]
   public static int antalsamma(String a, String b){
         int längd = Math.min(a.length(),b.length());
         int i=0;
         for(;i<längd;i++){
           if(a.charAt(i)!= b.charAt(i))
              break;
         }
      return i;
     }[/COLOR]
   private static final BigDecimal EIGHT = new BigDecimal(8);
   private static final BigDecimal TEN = new BigDecimal(10);
   private static final BigDecimal THREE = new BigDecimal(3);
   private static final BigDecimal FIF = new BigDecimal(15);
[COLOR="Blue"]   
[SIZE="4"][B]//the sqrt method[/B][/SIZE]
public static BigDecimal sqrt(BigDecimal S, MathContext mc){
     MathContext mode = new MathContext(mc.getPrecision()+2);
     BigDecimal y = new BigDecimal(0);
     BigDecimal x0 = new BigDecimal(0);
     BigDecimal x1 = new BigDecimal(1/Math.sqrt(S.doubleValue()));
     while(antalsamma(x0.toPlainString(),x1.toPlainString())<mc.getPrecision()){
      x0 = x1;
      y = S.multiply(x0.multiply(x0,mode),mode);
      x1 = x0.divide(EIGHT,mode).multiply(FIF.subtract(y.multiply(TEN.subtract(THREE.multiply(y,mode)),mode)),mode).abs();
     }
     return x1.multiply(S,mc);
   }[/COLOR]
}

so my question now is...Is there a faster way to count with decimals?! I have seen programs which are abel to count PI with 10^6 decimals in just a few seconds... how can this be possible ... please HELP!