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# how n(20*20 matrix) can obtain

Asked by vipul utsav on 28 Dec 2012
mean(s./n)=0.5
s=  1  2  3  4  5 ...20
20 19 18 17 16....1
1  2  3  4  5 ...20
20 19 18 17 16....1
1  2  3  4  5 ...20
20 19 18 17 16....1
...................
...................
20 19 18 17 16....1

s is a 20*20 matrix and it is fix; how n(20*20 matrix) can obtain such it follow above equation.

Image Analyst on 28 Dec 2012

You're posting enough now that you should learn how to highlight your code and click the {}Code button to format your code. Make sure there is a blank line before the first line of code though.

Image Analyst on 28 Dec 2012

You don't click {}Code first. If you do that, you get that useless "if true" like you just did. Just do what I said: make sure there's a blank line before your code, then highlight all your code (even intermediate blank lines if it's a long bit of code), then click {}Code.

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Answer by Image Analyst on 28 Dec 2012

It's trivial. Just solve the equation for n! You'll find it's twice s. Here's proof:

% Construct s.
s2rows = [1:20;20:-1:1];
s = repmat(s2rows, [10,1])
% Here's n.  It's just twice s!
n = s /0.5
% Proof that the mean = 0.5
theMean = mean2(s ./ n)

Jan Simon on 28 Dec 2012

@Vipul: No, "s" has exactly the same fixed matrix as in your question. Why do you think, that "s" is changed?

Btw, accepting an answer means, that it has solved your problem. Therefore the number of readers will be much smaller than for a thread without an accepted answer.

Image Analyst on 28 Dec 2012

And it doesn't matter WHAT s is. It could be anything at all. Just look at the equation - it's really basic math. No matter what s is, s over (2s) will be 1/2 for every single element, and thus give you a mean of 0.5. Is there something either I or you are not understanding here?

vipul utsav on 29 Dec 2012

i am really sorry, i did mistake,i misunderstand,,, it's 100% right answer