How do I specify the diagonal elements of a matrix?

I have some values, taken from another matrix. How do I specify them to be the diagonals of a new matrix?

[Hassan Rezaee]

You may use the function spdiags

Answer 1

[Matt Tearle]

To do a subscripted assignment into the diagonal of a matrix, you can use linear indexing:

A(1:n+1:end) = v

(where v is an n-element vector and n is the number of rows of A). So, for example,

A(1:n+1:end) = diag(B)

copies the diagonal of B into A.

[Changyong He]

I do not know why there is no comment. I have to say that it is the easiest way I have found. Excellent!

[Image Analyst]

Another way (again assuming you know n already):

A(logical(eye(n))) = diag(B)

[Dominick Arturi]

This works great for foward diagonals but how would one go about doing this to acess backwards diagonals?

[Walter Roberson]

n:n-1:end-n+1 for backwards diagonal on a square matrix

[Sebastien de Kort]

A(logical(fliplr(eye(n)))) = diag(B)

Answer 2

[Bruno Luong]

Take a look at DIAG function

    help diag