Is there any way to assign a value to the diagonals of a matrix (not just the main diagonal)?

I have a vector of values that I want to assign to the diagonals of a matrix. So for example, if my vector is

v = [ 2 7 8 9 5];

I want to make a matrix to have all the elements of the 1st diagonal equal to v(1), all the elements of the second diagonal equal to v(2), all of the elements of the third (and main) diagonal equal to v(8), and so on.

Is there any way to do that?

[mohammed]

Dear Alex

can you show your desired output?

like you want 5 matrix or only one Matrix.

[Danilo NASCIMENTO]

Let me understand... The order of your matrix should the length of your v vector... Is that what you mean? Actually I don't know what are you trying to perform... But this way you will not fill the matrix completely, the extremes of the inverse main diagonal will be left blank.

Answer 1

[Star Strider]

There is no ‘ v(8) ’. I assume you mean v(3) = 8.

This looks so kludgy that I’m almost ashamed to post it, but if I understand your question, it does what you want:

v = [ 2 7 8 9 5]
vc = size(v,2);
M = zeros(round(vc/2));
for k1 = 1:vc
    rvc2 = round(vc/2);
    if k1 <= rvc2 
        Mi = diag(ones(1,k1)*v(k1), rvc2-k1);
    elseif k1 > rvc2
        Mi = diag(ones(1,abs(rvc2+1-round(k1/2)))*v(k1), rvc2-k1);
    end
    M = M + Mi;
end

The matrix it produces is:

M =

       8.0000e+000     7.0000e+000     2.0000e+000
       9.0000e+000     8.0000e+000     7.0000e+000
       5.0000e+000     9.0000e+000     8.0000e+000

[Alex]

Thanks so much! That's exactly what I wanted!

[Star Strider]

My pleasure!

Answer 2

[mohammed]

Dear Alex

v = [ 2 7 8 9 5];
for i = 1:length(v)
b{i} = eye(3)*v(i)% 3 is the size of identity Matrix 
end

i hope it will help you.

[Alex]

Hi, thanks for your answer! I actually wanted them all in one matrix, but I did not specify that previously. I am sorry for that, and I thank you for your help all the same.

Answer 3

[Roger Stafford]

It depends on which side you call the "first" diagonal. If you use the order sense of matlab's 'diag' function, the diagonal numbers increase from lower left to upper right, so the first diagonal would be on the lower left. With definition do:

 M = toeplitz(v(3:-1:1),v(3:5));

If you order them in the opposite direction, do:

 M = toeplitz(v(3:5),v(3:-1:1));

[Alex]

This also works, and is very simple! Thanks so much!