how n(20*20 matrix) can obtain

     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.

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.

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.

Answer 1

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)

here i needs s is fix,in your code s is change

i have s and i defined it in post, i do not require construct it, only i require n of 20*20 matrix.

@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.

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?

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