Write a MATLAB algorithm takes as input the vector x and computes C rowwise

Say I have a vector x in R^3, such that x = [1 2 3]. I want to form from x, a matrix C = [1 2 3; 3 1 2; 2 3 1]. So, basically, the pattern here is that the first row of C is the vector itself, then the last entry of the first row is the first entry of the second row and the numbers (1 and 2) get shifted, and then the last entry of the second row is the first entry of the third row and the numbers (3 and 1) get shifted.

I want to write a general algorithm for any vector x in R^n, so this is what I have written:

function [C] = rowwise(x)

n = length(x);

C(1,:) = x;

for i = 2:n

for j = 1:n

C(i,j) = C(i-1,"?");

end

end

I don't know what to put instead of the question mark. And is my algorithm correct? Any other ways, please? And how to compute that same matrix C but columnwise? Thank you

Answer 1

[KSSV]

Read about circshift.

[Pascale Bou Chahine]

I read about it. Can you tell me how to put it in my algorithm please?

[KSSV]

C = [1 2 3] ;
n = length(C) ; 
iwant = zeros(n) ;
iwant(1,:) = C ;
for i = 2:n
  iwant(i,:) = circshift(iwant(i-1,:),1) ; 
end

[Pascale Bou Chahine]

And how to write an algorithm to get the same matrix C, but columnwise and not rowwise?

[KSSV]

You can use transpose ..