How do I reverse the order of a vector?

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..

Answer 1

[Andreas Goser]

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

[Ana Isabel Fernandez Sirgo]

thank you!

Answer 2

[Jan]

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.

[Walter Roberson]

That can be expressed more simply:

P = [0 1 7 6

2 3 5 4

4 5 3 2

6 7 1 0];

[Jan]

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

[Walter Roberson]

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

[Jim Dowd]

Funny stuff Jan Simon!

Answer 3

[Matt Fig]

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

[Walter Roberson]

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 4

[Walter Roberson]

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

[Andrew Newell]

That told him!

Answer 5

[Matt Fig]

Or, a one liner:

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

Answer 6

[Walter Roberson]

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

Answer 7

[Walter Roberson]

t = (0:2:6).'
trev = zeros(size(t));
trev(end:-1:1) = t;
P = [t, t+1, trev+1, trev];

Answer 8

[Walter Roberson]

for K = 1 : 4
  t(K) = 2*(K - 1);
end
for K = 1:length(t)
  trev(K) = t(end+1-K);
end

etc.

Answer 9

[Padala Bhaskara Rao]

clc;
clear all;
close all;
x=zeros(4,4);
x(:,1)=[1 2 -1 -2];
l=length(x);
x(:,2)=[1 3 -1 -3];
k=1;
for i=3:4
    for j=1:4
        x(j,i)=x(l+1-j,k);
    end
        k=k+1;
end