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Mathematica For looping problem not getting answer

  1. May 24, 2017 #1
    Hi, I need some helps. I try to run the code below but its keep give me the value of intial value.
    Code (Matlab M):

    Q = 1415; \[Mu] = 1000; \[Sigma] = 500;
    double dx;
    double x;
    double fx;
    double fxplusdx;
    double I1;
    double I2;
    I1 = 0;
    I2 = 0;
    For[x = 0, x <= Q - dx, dx += 0.01,
     fx = PDF[NormalDistribution[0, 1], (
       InverseCDF[NormalDistribution[\[Mu], \[Sigma]],
         x] - \[Mu])/\[Sigma]];
     fxplusdx =
      PDF[NormalDistribution[0, 1], (
       InverseCDF[NormalDistribution[\[Mu], \[Sigma]],
         x + dx] - \[Mu])/\[Sigma]];
     I1 = I1 + 0.5*(x*fx + (x + dx)*fxplusdx)*dx;
     I2 = I2 + 0.5*(fx + fxplusdx)*dx]
    I1
    I2 [/code/

    Thank you in advance
     
    Last edited by a moderator: May 24, 2017
  2. jcsd
  3. May 24, 2017 #2

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF.

    Can you please describe in detail what the code is supposed to do?
     
  4. May 24, 2017 #3
    I want to find the final value of I1 and I2 using the for loop (from x=0 up to x=Q - dx).
    fx and fxplus dx is a PDF of normal distribution. When I run, I get final value I1, and I2 equal to 0.There's no changes from the initial value.
     
  5. May 24, 2017 #4

    jedishrfu

    Staff: Mentor

    I would place print statements in the loop for each variable referenced and run it to see how they changed.

    Print x, dx, fx, fxplus ...i1, i2

    It also looks like x is always zero. I don't see anywhere where it's being changed in your loop. Did you mean to use dx instead of x or did you mean to say x+=dx?

    In Java the for loop looks like this

    For( initial value; loop test; increment value)

    So in your case I'm wondering if you meant something like this

    for(x=0; x<Q; x+=dx)

    I also found this Mathematica reference of loops

    https://reference.wolfram.com/language/tutorial/LoopsAndControlStructures.html
     
    Last edited: May 24, 2017
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