help with while loop

Hi, I'm trying to find the maximum value of n for which the error is 0.001875. Im not sure if my code is right. I have to functions. They are related as the output of one is the input of the other. Any suggestions? I keep on getting n=0

n=0;
[CC, ww]=fourier_analysis(step_signal1,1,n);
[ss,tt]=fourier_synthesis(CC,1,1,16384);

while (ER>.001875)
   ER=0.3750-mean(ss.^2);
   n=n+1;
end
display(n)

Answer 1

[Geoff Hayes]

Andrea - how is ER initialized? Since you are iterating until a certain condition is met (i.e. ER<=0.001875), your two functions should be within the while loop so that ss changes at each iteration

 ER = 1;
 maxIters = 100;
 n=0;
 while (ER>.001875 && n<=maxIters)
     [CC, ww]=fourier_analysis(step_signal1,1,n);
     [ss,tt]=fourier_synthesis(CC,1,1,16384);
     ER=0.3750-mean(ss.^2);
     n=n+1;
 end
 display(n)

Note how the maxIters local variable is used to control the maximum number of iterations of your while loop. We do this so that we do not become stuck in an infinite loop.

[Andrea]

wow that worked pretty well. I just don't understand why the need to initialize ER=1 and how would you pick a value for maxIters? Thanks a lot!!

[Andrea]

Im asking because I changed the value of maxIters and got different answers

[Geoff Hayes]

Andrea - you must have chosen something for ER because without it being initialized, you should see an error message similar to

 Undefined function or variable 'ER'.

I chose 1 only because it is larger than your threshold.

If you are getting different answers for different maxIters then that is because your ER is not falling below the 0.001875 threshold. You should plot the values of ER from each iteration to see what is happening over time. Are they getting smaller, larger, fluctuating? Do they appear to converge to some number?