Determine Expression

2011 11 21
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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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bym
bym 2011-11-21

0 个投票

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

2 个投票

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
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Sven
Sven 2011-11-21
We already have the question. We *don't* have any idea what you've tried so far. You say "I have no idea where to start". Please start by answering the following:
1. Do you have MATLAB installed?
2. Have you read the "Getting Started" chapter? (it's a *great* place to start)
3. Do you know how to write a "for loop"?
4. Please show us your "for loop" for this question and describe what you want it to do.
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
Sven
Sven 2011-11-21
Bobby, please stop deleting your comments.
Bobby
Bobby 2011-11-21
is my for loop correct? What about my results?
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

0 个投票

Have you read the MATLAB Getting Started Guide? There are plenty of examples on using loops.

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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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