what's wrong with the code?

Hi, what's wrong with the following code?

=========================================================================================================x=pi/4; n=2; sum=2; while(1) m=2*n-1; sumnew=sum+(-1)^(n-1)*x^m/factorial(m); error=(sumnew-sum)/sumnew; n=n+1; sum=sumnew; if error<0.001; break end end

Answer 1

[Andrei Bobrov]

Try it

x= pi/4;
n = 2;
sum1 = 2;
er = 1;
while  abs(er) > 0.001
    m = 2*n-1;
    sumnew = sum1+(-1)^(n-1)*x^m/factorial(m);
    er = (sumnew-sum1)/sumnew;
    n = n+1;
    sum1 = sumnew;
end

Answer 2

[Roger Stafford]

If you were trying to calculate sin(pi/4), you started with the wrong values for n and sum1. For sin(pi/4) it should be the following. (As yours stands, it computes 2+sin(pi/4)-pi/4.)

   x=pi/4; 
   n=1;    % <-- Start with n = 1
   sum1=0; % <-- Start with sum1 = 0
   while(1)
     m=2*n-1;
     sumnew=sum1+(-1)^(n-1)*x^m/factorial(m);
     error=abs((sumnew-sum1)/sumnew);  % <-- Also this should be absolute value
     n=n+1;
     sum1=sumnew;
     if error<0.001; break end 
   end

[Note: Like Andrei, I substituted 'sum1' for 'sum' because the latter symbol is reserved for matlab's 'sum' function.]

[B]

Thanks everyone. But in the following code where I have only changed while(1)-->while.., I'm getting the correct answer. Why is that?? ================================================================================= x=pi/4; sum1=x; n=2; error=5; while error>0.001 m=(2*n)-1; sumnew=sum1+(-1)^(n-1)*x^m/factorial(m); error=(abs(sumnew-sum1)/sumnew); n=n+1; sum1=sumnew; end display(sumnew)

================================================================================= I've also tried your codes, but MATLAB was stuck, could you plz check that? Thanks a lot for your help.

[B]

I'm not sure if the problem is related to the computer it self. It's very slow right now..

[B]

First code is working now.. Thanks Andrei Bobrov