Determine Expression

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Bobby
Bobby 2011-11-21
Write a program (using a loop) the dertimes the expression: sqrt 12 Sigma (m on top) (n=0 on bottom) ((-1/3)^n) / (2*n+1) Run the program with m=5 m=10 and m=20. Compare the results with pi (Use Long format).
this is what I have done
format long
S=0 m=input('Input a value for m=')
for n=0:m S(1:m)=sqrt(12)*(S+((-1/3)^n)/(2*n+1))
end
not sure if this is right
run program for m=5 m=10 m= 20
my results m =
5s =
Columns 1 through 4
3.464101615137754 3.464101615137754 3.464101615137754 3.464101615137754Column 5
3.464101615137754s =
Columns 1 through 4
11.615099820540248 11.615099820540248 11.615099820540248 11.615099820540248
Column 5
11.615099820540248
s =
Columns 1 through 4
40.312866084211663 40.312866084211663 40.312866084211663 40.312866084211663
Column 5
40.312866084211663
s =
1.0e+002 *
Columns 1 through 4
1.396295359331753 1.396295359331753 1.396295359331753 1.396295359331753Column 5
1.396295359331753s =
1.0e+002 *
Columns 1 through 4
4.836956528011152 4.836956528011152 4.836956528011152 4.836956528011152Column 5
4.836956528011152s =
1.0e+003 *
Columns 1 through 4
1.675569596143254 1.675569596143254 1.675569596143254 1.675569596143254Column 5
1.675569596143254

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采纳的回答

bym
bym 2011-11-21
the multiplication of sqrt(12) should occur outside the loop. Also do not include S in the summation:
for n = 0:m
s(n+1) = (-1/3)^n/(2*n+1);
end
now you have a vector of values you can sum & multiply by sqrt(12)

更多回答（2 个）

Jan
Jan 2011-11-21
Could we have an idea?
Do you have a computer? Is Matlab installed? Did you read the getting started chapters already? Do you know, what a loop is, especially a FOR loop? Have you aksed Google for some details already?
You've posted the homework question and we cannot post the running code. So what kind of help do you expect?
  6 个评论
显示 4更早的评论
Sean de Wolski
Sean de Wolski 2011-11-21
Are your results correct? Do they meet the constraints of the problem? If they do, I would hazard a guess they're correct!
Walter Roberson
Walter Roberson 2011-11-21
Your loop is wrong, and your results are wrong.
Re-read the question. How many elements are output from a summation ? How many output elements do you have?

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Wayne King
Wayne King 2011-11-21
Have you read the MATLAB Getting Started Guide? There are plenty of examples on using loops.
  1 个评论
Bobby
Bobby 2011-11-21
this is what I have done
format long
S=0
m=input('Input a value for m=')
for n=0:m
S(1:m)=sqrt(12)*(S+((-1/3)^n)/(2*n+1))
end
not sure if this is right

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