What is the problem in these code?

Question

Selin Soguksu 2012-12-19

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关闭： MATLAB Answer Bot 2021-8-20

Hello friends, I have a code like this:

for x=1:50
  Nrows=size(orj_matr,1)
  new_matr=randperm(Nrows)
  new_matr=new_matr(1:50)
  a(:,:,x)=orj_matr(new_matr,:)
end

When I wrote this codes to MATLAB, I have 50 different (50 rows-10 columns) matrices. Like this:

a(:,:,1) , a(:,:,2), a(:,:3), …………a(:,:,50)

And I want to calculate f1 and f2 for these 50 different matrices. When I wrote like this there was an error saying “Indexing must appear last in an index expression”.

f1=sum(a(:,:,x) (:,1:2:end),2);
f2=sum(a(:,:,x) (:,2:2:end),2);

What is the mistake in these codes? Please help me...

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Jan 2012-12-19

编辑：Jan 2012-12-19

It would be useful if you explain, what the the expression "a(:,:,x) (:,1:2:end)" should do. As long as it is no valid Matlab syntax, a suggestion for improvement requires guessing what you want to achieve. And an answer based on guesses can be worse than no answer.

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Answer 1

Jürgen 2012-12-19

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编辑：Jürgen 2012-12-19

Hi,

sum(a(:,:,x) (:,1:2:end),2); is not correct , I think What do you want to do there? '(:,1:2:end)' is referring to the index and it put at the right place regards,J

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José-Luis 2012-12-19

在 MATLAB Online 中打开

I would recommend you read up on indexing.

a(:,:,x) (:,1:2:end)

is not a valid expression. I am guessing that what you want is something along the lines

squeeze(sum(a(:,1:2:end,:),2))

Also, please edit your code to make it more readable. That might attract more answers.

Jürgen 2012-12-19

编辑：Jan 2012-12-19

to sum all even columns:sum(A(:,2:2:end)) for odd columns: sum(A(:,1:2:end))

Answer 2

Selin Soguksu 2012-12-19

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Thanks all of you for the answers and comments. I saw my mistake and correct my codes. Now it works good. I know my codes are not clear enough, because I am very new with MATLAB. And also sometimes I can't tell you what I want because of my poor English.