Different Values, Constanst Results in Mathematica

[EngWiPy]

Hello,

I have the following piece of code in Mathematica:

Na =.;
Q =.;
A = 23;
Q = 15;
Na = 21;
MGF[s_, gC_] := 1/(1 - gC*s);
a[n_] := If[n == 0, 2, 1];
For[SNRdB = 0, SNRdB <= 40, SNRdB = SNRdB + 2, SNR = 10^(SNRdB/10);
 gC = 0.5*SNR;
 
 Print[SetPrecision[Pout = ((2^-Q*E^(A/2))/SNR*\!\(
\*UnderoverscriptBox[\(\[Sum]\), \(q = 0\), \(Q\)]Binomial[Q, q]*\(
\*UnderoverscriptBox[\(\[Sum]\), \(n = 0\), \(Na + q\)]
FractionBox[
SuperscriptBox[\((\(-1\))\), \(n\)], \(a[n]\)] Re[
\*FractionBox[\(MGF[\(-
\*FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]\), gC]\), 
FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]]]\)\)) + (E^-A/(
       1 - E^-A) + (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]]]

Despite the variable "SNR" changed in each iteration of the for loop, the printed result is the same in all iterations. Why is this?

Thanks in advance

 

[Dale]

That is correct. The formula you posted does in fact give the same value for different values of SNRdB.

 

[EngWiPy]

That is correct. The formula you posted does in fact give the same value for different values of SNRdB.

Thank you DaleSpam, your answer made me double check and think about the problem, and the problem was a logical one. Some parameters must be fixed and others must be changed, while what I did was that I changed all variables altogether.

Best regards

 

[Dale]

Ahh, ok. One thing you might think of doing is setting up a function that takes all of the parameters. That makes evaluating it at different values much easier.

 

[EngWiPy]

Ahh, ok. One thing you might think of doing is setting up a function that takes all of the parameters. That makes evaluating it at different values much easier.

Execuse me, I didn't get you. Can you elaborate please.

 

[Dale]

For example:

f[n_, Q_, q_, A_, gC_, Na_, SNR_] := 
(-1)^n/a[n] ((2^-Q*E^(A/2))/SNR*\!\(
\*UnderoverscriptBox[\(\[Sum]\), \(q = 0\), \(Q\)]\(Binomial[Q, q]*\(
\*UnderoverscriptBox[\(\[Sum]\), \(n = 0\), \(Na + q\)]
FractionBox[
SuperscriptBox[\((\(-1\))\), \(n\)], \(a[n]\)] Re[
\*FractionBox[\(MGF[\(-
\*FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]\), gC]\), 
FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]]]\)\)\)) + (E^-A/( 
      1 - E^-A) + (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 \((Na + q + 1)\)\), \(2*SNR\)]]]\)\))

Then your for loop is cleaner and easier to debug since you just call f in each iteration with different values for the arguments.

 

[EngWiPy]

For example:

f[n_, Q_, q_, A_, gC_, Na_, SNR_] := 
(-1)^n/a[n] ((2^-Q*E^(A/2))/SNR*\!\(
\*UnderoverscriptBox[\(\[Sum]\), \(q = 0\), \(Q\)]\(Binomial[Q, q]*\(
\*UnderoverscriptBox[\(\[Sum]\), \(n = 0\), \(Na + q\)]
FractionBox[
SuperscriptBox[\((\(-1\))\), \(n\)], \(a[n]\)] Re[
\*FractionBox[\(MGF[\(-
\*FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]\), gC]\), 
FractionBox[\(A + \((2*Pi*I*n)\)\), \(2*SNR\)]]]\)\)\)) + (E^-A/( 
      1 - E^-A) + (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 \((Na + q + 1)\)\), \(2*SNR\)]]]\)\))

Then your for loop is cleaner and easier to debug since you just call f in each iteration with different values for the arguments.

Yes, you are right. I will try do this. Thanks