creating a diagonal matrix?

Hi,

I want to create a diagonal matrix which has the elements like this: q1,q1,q2,q2,...,qm,qm

q is a function and has m different values for m different x-values

Could anyone help me please?

Thank you!

Answer 1

[Simon]

Hi!

diag(q)

[FULYA SEREF]

thank you very much but as you see I have the elements who are the same for two times. I suppose I need a loop. I can't enter these values by hand. Because first I will define the function q. I need m different values of q for m different x values. And I have to create a matrix whose diagonal is for example; q(1),q(1),q(2),q(2), ,....,q(m),q(m).

[Simon]

So, if you have your function q, what will be the output? Is it a m-element vector? Or just a scalar value?

If you have your m-element vector X, you can do

ind = 1:m;
ind = [ind; ind];
diag(X(ind(:)))

If you get scalars only you have to create it in a loop.

Answer 2

[Sean de Wolski]

diag(q(1,2,3))

And for more info:

doc diag

[FULYA SEREF]

thank you very much but as you see I have the elements who are the same for two times. I suppose I need a loop. I can't enter these values by hand. Because first I will define the function q. I need m different values of q for m different x values. And I have to create a matrix whose diagonal is for example; q(1),q(1),q(2),q(2), ,....,q(m),q(m).

Answer 3

[Jos (10584)]

Like this?

    q = [10 20 30] ;
    q = q(floor(1:.5:numel(q)+.5)) % expand (there are many other ways to do this!)
    diag(q)