Create a matrix with elements clockwise

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Alexis Pelet on 16 Jun 2021
Commented: Alexis Pelet on 16 Jun 2021
Hello,
I would like to create a [m,n] size matrix in which the ID of the elements are created clockwise/counterclockwise.
The first element should starts in (1,1).
For example, for a matrix of size [5,8] (meaning 40 elements in total) we should have this final matrix:
This should be the result in Matlab:
Thank you in advance for your answers !
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Accepted Answer

Stephen23 on 16 Jun 2021
Edited: Stephen23 on 16 Jun 2021
More efficient:
M = spiral2(5,8)
M = 5×8
1 22 21 20 19 18 17 16 2 23 36 35 34 33 32 15 3 24 37 38 39 40 31 14 4 25 26 27 28 29 30 13 5 6 7 8 9 10 11 12
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Alexis Pelet on 16 Jun 2021
It's perfect! I will not forget to mention your name in the algorithm I am creating, thank you very much!

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More Answers (1)

Joseph Cheng on 16 Jun 2021
While probably not the most efficient way you can fill in edges like i've done here:
clc;clear all
x = zeros(5,8); %generate matrix to be filled with 0's
totN = numel(x);
indexes = 1:totN; %get values to fill in the spiral, here 1:total number for review
cnum=1; %column number to fill in
while numel(indexes)~=0 %while there is still numbers to fill in
for ind = 1:4 %rotate 4 times for 4 edges before next spiral in
zindex = find(x(:,cnum)==0); %for the leading left hand edge see which values are 0
x(zindex,cnum)=indexes(1:numel(zindex)); %fill in where there are 0's by the next 1:#zeros
indexes(1:numel(zindex))=[]; %remove values used from the list
x = rot90(x,-1); %rotate whole matrix so we're just working on a consistant edge
end
disp(x) %display matrix
cnum=cnum+1; %now we've rotated 4 times we're back to original orientation and need to spiral in (next col over)
end
1 22 21 20 19 18 17 16 2 0 0 0 0 0 0 15 3 0 0 0 0 0 0 14 4 0 0 0 0 0 0 13 5 6 7 8 9 10 11 12 1 22 21 20 19 18 17 16 2 23 36 35 34 33 32 15 3 24 0 0 0 0 31 14 4 25 26 27 28 29 30 13 5 6 7 8 9 10 11 12 1 22 21 20 19 18 17 16 2 23 36 35 34 33 32 15 3 24 37 38 39 40 31 14 4 25 26 27 28 29 30 13 5 6 7 8 9 10 11 12
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Alexis Pelet on 16 Jun 2021
Even if you say it's not the most efficient way to do it, your code does the job! Thank you!!

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