Problem with a code

Hi, I need to find out the minimum N so that Eg<10^(-7). I got that N=199...and it's to much... Can anyone help me what is the problem with my code?

Thanks,

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[James Tursa]

Please don't post your code as an image ... it forces the reader to type your code in by hand in order to run it, and nobody wants to do that. Please re-post your code as text and use the { } Code button to format it.

[david david]

h=1/2000;
er= 10^(-7);
N=1;
eg=10;

while (eg>er)
    sumup=0;
    sumdown=0;

      for m=0:5000,
          nsum=0;
          for n=0:N,
          nsum=nsum+(((32/((pi).^3)).*(((-1)^n)/((2.*n+1).^3).*(cos(((2*n+1)/5)*(pi)*m*h)))));
          end
          sumup=sumup+(abs(nsum-(1-(2.*m.*h/5).^2)).^2);
          sumdown=sumdown+((1-(2.*m.*h/5).^2).^2);
      end 
      eg=sqrt((sumup)/(sumdown));
      N=N+1;
  end

N;

Answer 1

[Stephen23]

Here is a solution using no loops, and only vectorized code:

hy = 1/2000;
mv  = 0:5000;
den = sqrt(sum((1-(2/5*mv*hy).^2).^2));
pfx = @(nv) (-1).^nv ./ (2*nv + 1).^3;
trg = @(nv) bsxfun(@times, (2*nv+1)/5, pi*mv*hy);
foo = @(nv) bsxfun(@times, pfx(nv), cos(trg(nv)));
bar = @(nv) sqrt(sum((32/pi^3 * sum(foo(nv)) - (1-(2/5*mv*hy).^2)).^2));
fun = @(N) bar((0:N)') / den;

First lets take a look at the function:

>> X = 1:300; % range of N values
>> Y = arrayfun(fun, X);
>> semilogy(X,Y)

And now the first value <1e-7 occurs for an N of:

>> Z = Y<1e-7;
>> X(find(Z,1,'first'))
ans =
   198

[david david]

Thanks