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Mathematica: Printing Numeric Result

  1. Jun 12, 2012 #1
    Hey,

    So im fairly new to Mathematica (and the physics forums too). I am having a problem with mathematica not calculating the numeric result to an very complex integral. My question is, how do I force it to evaluate the integral as a number? I'm assuming that the integral of a square root is possible in mathematica as i checked the help files and it seems to suggest it is. I have tried the evaluation both with and without using n[A] which seems to be the suggested method of forcing a numeric evaluation.

    K=1
    R=1
    VM=1
    L=1
    radius=1
    z=-0.000000*x^6 - 0.000000*x^5 + 0.000049*x^4 + 0.000115*x^3 - 0.018528*x^2 - 0.033042*x + 2.964166
    dzdx=D[z,x]
    absdzdx=Abs[dzdx]
    sqrtfactor=Sqrt[1+dzdx^2]
    A=2*Pi*K*R*VM*L*(Integrate[(6.5+4.56*(absdzdx)+0.654*(absdzdx)^2)*x*sqrtfactor,{x,0,r}])*((2*Pi*\!\(
    \*SubsuperscriptBox[\(\[Integral]\), \(0\), \(r\)]\(\((x*sqrtfactor)\) \[DifferentialD]x\)\))/10000)


    I have tried to break up the calculations so that mathematica doesnt take to long to calculate it but it still seems to take at least 3 or 4 mins of running before it displays an answer. The variables do unfortunately need to stay seperate as they will be changed. I apologise in advance if it is just some stupid error of mine.
     
  2. jcsd
  3. Jun 13, 2012 #2
    If you can supply a numeric value for r, perhaps like this

    r = 1;

    then this

    In[1]:= A=2*Pi*K*R*VM*L* NIntegrate[((6.5+4.56*absdzdx+0.654*absdzdx^2)* x*sqrtfactor),{x,0,r}]*
    2*Pi/10000*NIntegrate[x*sqrtfactor,{x,0,r}]]

    Out[1]= 0.00669876

    evaluates in a fraction of a second.

    If you cannot provide a numeric value for r then I doubt you will get a satisfactory answer.
     
    Last edited: Jun 13, 2012
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