Create a matrix with elements clockwise

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 !

Answer 1

[Stephen23]

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

[Alexis Pelet]

It's perfect! I will not forget to mention your name in the algorithm I am creating, thank you very much!

Answer 2

[Joseph Cheng]

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

[Alexis Pelet]

Even if you say it's not the most efficient way to do it, your code does the job! Thank you!!