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Help with matlab program for cos(x)

  1. Aug 30, 2010 #1
    1. The problem statement, all variables and given/known data

    The function cos(x) can be approximated using the following series expansion:
    1df491c1c760cda57c0f4f71cd2f191.png

    Write a MATLAB function called seriesCos that takes a single scalar argument, x, uses the above formula to compute cos(x), and returns the result. Your function should use a while loop and continue adding terms to the series until the absolute value of the difference between successive iterations is less than 1.e-6. MATLAB functions that may prove useful include factorial() and abs().

    2. Relevant equations
    i can't get it to work and i'm not sure what I am doing wrong.It's not going through the loop or anything


    3. The attempt at a solution
    function y=seriesCos(x);
    %calculate cos(x) through a series
    %user call seriesCos(x,n)
    %x is number to evaluate n is desire cycles through series
    x=input ('Enter x to be evalute: ');
    ser=1;
    sum=0;
    n=1;
    er=0.0;
    while er>=1e-6
    an=(-1)^n*x^(2*n)/(factorial(2*n));
    sum=ser;
    ser=sum+an;
    n=n+1;
    er=abs((ser-sum)/(ser));
    end
    disp (ser)
    disp (er)
     
  2. jcsd
  3. Aug 31, 2010 #2
    look at the line in which you start the while loop and you should see something wrong

    what is er defined to be?
     
  4. Aug 31, 2010 #3

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    You are right, it's not going through the loop, because you are telling it not to:

    Code (Text):

    er=0.0;
    while er>=1e-6
     ...
     
    I suggest setting er to something larger than 1e-6 to start with :P
     
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