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Homework Help: Simpson's 3/8's rule

  1. Nov 19, 2004 #1
    I am having problems in Numerical Methods with Simpson's 3/8 rule of integration. Of course, this is computer driven. The code that I have written for Matlab (SV7) goes as such:

    1) function simpson38(f,n,a,b)
    2) h = (b-a)/n;
    3) x = a;
    4) sum = f(x);
    5) for i = 1:3:(n-3)
    6) x = x + h;
    7) sum = sum + 3 * f(x);
    8) x = x + h;
    9) sum = sum + 3 * f(x);
    10) x = x + h
    11) sum = sum + 2* f(x);
    12) end
    13) x = x + h;
    14) sum = sum + 3 * f(x);
    15) x = x + h;
    16) sum = sum + 3 * f(x);
    17) x = x + h
    18) sum = sum + f(b);
    19) I = (b-a) * sum/(8*n)


    f = the function to be integrated, n = number of points, h = the stepsize, i is a counter, and sum is the sum of the values. a and b are the endpoints. I = the final integrated value.

    If I am reading the book right, the middle points are given a weight of 3/8 each, with the end points given a weight of 1/8. With that in mind, line 11 should be weighted 2/8 (end point from 2 directions) unless it is the final endpoint.

    What am I missing?

    Thanks
    Bill
     
  2. jcsd
  3. Nov 19, 2004 #2
    Tell me the problem. The code does not give correct answer?
    I think you need to multiply your final sum by 3/8 not just 1/8 (hence the name 3/8 rule).
     
  4. Nov 19, 2004 #3
    kakarukeys,

    Thank you, you are spot on.

    Bill
     
  5. Nov 10, 2011 #4
    why is x=a; showing an error when i tried to use this code
     
  6. Nov 2, 2012 #5
    Hello people i m looking or Simpsons 3/8th rule which can be used for Normal table calculation in C++....need urgent help
     
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