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Solving equation in Mathematica

  1. Aug 9, 2009 #1
    Hello,

    I have the following code to find the parameters Na and Q that make the expression equals [tex]10^{-10}[/tex]:

    Code (Text):
    Na =.;
    Q =.;
    MGF[s_, gC_] := 1/(1 - gC*s);
    SNRdB = 0;
    SNR = 10^(SNRdB/10);
    gC = 0.5*SNR;
    p = gA*gB;
    A = 23;
    Solve[((E^(A/2)*2^-Q)/SNR \!\(
    \*UnderoverscriptBox[\(\[Sum]\), \(q = 0\), \(Q\)]\(-
    \*SuperscriptBox[\(1\), \(Na + q + 1\)]\)*Binomial[Q, q]*Re[
    \*FractionBox[\(MGF[\(-
    \*FractionBox[\(A + \((2*Pi*I \((Na + q + 1)\))\)\), \(2\ SNR\)]\),
              gC]\),
    FractionBox[\(A + 2*Pi*I \((Na + q + 1)\)\), \(2\ SNR\)]]]\)) ==
       10^-10, {Na, Q}]
    But it doesn't work? Anyone have any idea about how solving this equation?

    Thanks in advance
     
  2. jcsd
  3. Aug 9, 2009 #2

    Dale

    Staff: Mentor

    There are not analytical solutions for all equations. Functions like Solve, Reduce, DSolve, etc. will not always be able to find a solution. In such cases you can only find numerical solutions using e.g. FindRoot.
     
  4. Aug 9, 2009 #3
    Thanks DaleSpam for replying,

    So, you are saying that If I replace the "Solve" command by "FindRoot", I may get a result?

    Regards
     
  5. Aug 9, 2009 #4

    Dale

    Staff: Mentor

    The syntax for FindRoot is a little different than for Solve. You should use the help menu to find the new syntax and some examples.
     
  6. Aug 10, 2009 #5
    Ok, I will. Thanks again
     
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