How do I reverse the order of a vector?

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Umer
Umer 2011-2-9
评论： Ana Isabel Fernandez Sirgo 2020-11-5
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..

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回答（9 个）

Andreas Goser
Andreas Goser 2011-2-9
I think you are looking for commands like flipud and fliplr, right?
Jan
Jan 2011-2-9
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.
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Walter Roberson
Walter Roberson 2011-2-10
I think of it as a way of differentiating between those who learn and those who copy without understanding.

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Matt Fig
Matt Fig 2011-2-10
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 个评论
Walter Roberson
Walter Roberson 2011-2-10
I was working on fitting it to a 100'th order polynomial, but discovered that any order beyond 23 gives absolutely completely wrong answers!

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Walter Roberson
Walter Roberson 2011-2-9
t = (0:2:6).'; P = [t, t+1, 7-t, 6-t];
Matt Fig
Matt Fig 2011-2-10
Or, a one liner:
reshape(permute(reshape([0:7 7:-1:0],2,4,2),[2,1,3]),4,4)
Walter Roberson
Walter Roberson 2011-2-9
t = (0:2:6).';
trev = t(length(t):-1:1);
P = [t, t+1, trev+1, trev];
Walter Roberson
Walter Roberson 2011-2-9
t = (0:2:6).'
trev = zeros(size(t));
trev(end:-1:1) = t;
P = [t, t+1, trev+1, trev];
Walter Roberson
Walter Roberson 2011-2-9
for K = 1 : 4
t(K) = 2*(K - 1);
end
for K = 1:length(t)
trev(K) = t(end+1-K);
end
etc.
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

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