MATLAB Answers

Umer

How do I reverse the order of a vector?

Asked by Umer
on 9 Feb 2011

Generate a 4x4 matrix P, whose first column is an array of 0, 2, 4 and 6; second column is an array of 1, 3, 5, and 7; third is the second column in reverse order and fourth column is the first column in reverse order. I want to use Reverse function or something like that..

  0 Comments

8 Answers

Answer by Andreas Goser
on 9 Feb 2011

I think you are looking for commands like flipud and fliplr, right?

  0 Comments


Jan Simon
Answer by Jan Simon
on 9 Feb 2011

It would be an inefficient idea to use a function to create a 4x4 matrix with fixed values!

P = [0, 1, 7, 6; ...
     2, 3, 5, 4; ...
     4, 5, 3, 2; ...
     6, 7, 1, 0];

Now this homework is solved. Kind regards to your teacher.

  4 Comments

Jan Simon
on 9 Feb 2011

I think this is more prone to errors and confuses beginners.

Walter Roberson
on 10 Feb 2011

I think of it as a way of differentiating between those who learn and those who copy without understanding.

Jim Dowd
on 10 Feb 2011

Funny stuff Jan Simon!


Answer by Matt Fig
on 10 Feb 2011

Walter, I am shocked that you didn't include the obvious nested FOR loop.

cnt = 0;
for ii = 1:2,
    for jj = 1:4
        A(4-jj+1,4-ii+1) = cnt;
        A(jj,ii) = cnt;
        cnt = cnt + 2;
    end
    cnt = 1;
end

  1 Comment

Walter Roberson
on 10 Feb 2011

I was working on fitting it to a 100'th order polynomial, but discovered that any order beyond 23 gives absolutely completely wrong answers!


Answer by Walter Roberson
on 9 Feb 2011

t = (0:2:6).'; P = [t, t+1, 7-t, 6-t];

  1 Comment

Andrew Newell
on 10 Feb 2011

That told him!


Answer by Matt Fig
on 10 Feb 2011

Or, a one liner:

reshape(permute(reshape([0:7 7:-1:0],2,4,2),[2,1,3]),4,4)

  0 Comments


Answer by Walter Roberson
on 9 Feb 2011
t = (0:2:6).';
trev = t(length(t):-1:1);
P = [t, t+1, trev+1, trev];

  0 Comments


Answer by Walter Roberson
on 9 Feb 2011
t = (0:2:6).'
trev = zeros(size(t));
trev(end:-1:1) = t;
P = [t, t+1, trev+1, trev];

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Answer by Walter Roberson
on 9 Feb 2011
for K = 1 : 4
  t(K) = 2*(K - 1);
end
for K = 1:length(t)
  trev(K) = t(end+1-K);
end

etc.

  0 Comments


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