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Bisection method by c

  1. Feb 7, 2009 #1
    here is the c program for arriving at a solution using bisection method.
    The ouputi s going infinte..pls help ....i think it has more of syntax errors than logical errors...

    Code (Text):

    main()
    {
        float a,b,c,x1,x2,x,series;
        double d;

        printf("enter a,b,c and x1(pos) & x2(neg)");
        scanf("%f%f%f%f%f", &a, &b, &c, &x1, &x2);

        read:

        x = (x1 + x2) / 2;
        series = a * x * x + b * x + c;
        d = fabs(series);

        if (d > 0.0001)
        {
            if (x * x1 < 0)
                x = x2;
            else
                x = x1;

            goto read;
        }
        else
        {
            printf("ans=%f", x);
        }

        return 0;
    }

     
     
    Last edited: Feb 7, 2009
  2. jcsd
  3. Feb 7, 2009 #2
    Code (Text):
    goto read;
    Arf!
     
  4. Feb 7, 2009 #3
    You will probably get some help faster my learning to format code so someone can read it.



    Code (Text):

    main()
    {
        float a,b,c,x1,x2,x,series;
        double d;

        printf("enter a,b,c and x1(pos) & x2(neg)");
        scanf("%f%f%f%f%f", &a, &b, &c, &x1, &x2);

        read:

        x = (x1 + x2) / 2;
        series = a * x * x + b * x + c;
        d = fabs(series);

        if (d > 0.0001)
        {
            if (x * x1 < 0)
                x = x2;
            else
                x = x1;

            goto read;
        }
        else
        {
            printf("ans=%f", x);
        }

        return 0;
    }
     
     
  5. Feb 7, 2009 #4
    okkk
    sry but thnx...
     
  6. Feb 7, 2009 #5

    rcgldr

    User Avatar
    Homework Helper

    Note that you reassign x each time at "read:" so the if statement assignements have no effect. I'm not famliar with the algorithm, but you probably should be assigning x1 or x2 in your if statement:

    read:
    x=(x1+x2)/2;
    ...
    if (x*x1<0) x2=x ; else x1=x;
    goto read;

    Would have been nice if the previous posts offered some constructive help.
     
  7. Feb 7, 2009 #6
    thnx.....i will try my best...
     
  8. Feb 7, 2009 #7
    It would be even nicer if you decided to keep your opinions on earlier posts to yourself. :wink:
     
  9. Feb 7, 2009 #8
    yeah...dude and guess what ...it would be much more nicer if u followed what u preach :wink: :wink:
     
  10. Feb 7, 2009 #9
    i edited my code..bt still isnt workin..wld b glad 2 recive ur help

    Code (Text):

    #include<stdio.h>
    #include<math.h>
    main()
    {float a,b,c,x1,x2,x,series;
    double d;



    printf("enter a,b,c and x1(pos) & x2(neg)");
    scanf("%f%f%f%f%f",&a,&b,&c,&x1,&x2);


    x=0;
    d=1;

     while(d>0.0001)
        {
          x=(x1+x2)/2;
         

         series=a*x*x+b*x+c;
         

         d=fabs(series);
         

             if(x*x1 < 0)
                 x2=x;
             else
                 x1=x;
        }

         

    printf("ans=%f",x);



    return 0;
    }
     
     
  11. Feb 8, 2009 #10

    rcgldr

    User Avatar
    Homework Helper

    The if statement should multiply the function(x1) * function(x), not x1 and x themselves. Using a new variable called series1:

    series = a*x*x + b*x + c;
    series1 = a*x1*x1 + b*x1 + c;
    ...
    if (series * series1) < 0) x2 = x; else x1 = x;
    ...

    Also note that the initial values for x1 and x2 need to be chosen so that

    a*x1*x1 + b*x1 + c > 0
    a*x2*x2 + b*x2 + c < 0

    A parabola would have to cross the x axis twice for this method to work, and there would be two possible answers. The initial values for x1 and x2 would have to chosen so that only one of the answers would occur in the range x1 .. x2.
     
    Last edited: Feb 8, 2009
  12. Feb 9, 2009 #11
    u r rite..series and series1 get multiplied and the main equation shld better not b quadratic..thnx...
     
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