# how can i write function to display matrix?

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hassan elkholy on 23 Dec 2020
Answered: Masoud Dorvash on 18 Jan 2021
how can i write function to display a zero matrix and its diagonal calculated by function
f(n) = f(n-1)+2f(n-2)+3
it has only one input n
Walter Roberson on 23 Dec 2020
If you start with an all-zero matrix then every element of the matrix will be the same for any given n, so it seems odd to talk about the diagonal.
You would need a matrix multiplication step to perturb the elements so that the diagonals were not all the same.

Masoud Dorvash on 18 Jan 2021
Hello,
You just need to use
D = diag(v);
This command will create a matrix with the elements of v on the main diagonal.
Try to first create your v vector (here in your example is f(n)) then put it there.
v = [1 6 2 14 1 8 46];
diag(v)
ans =
1 0 0 0 0 0 0
0 6 0 0 0 0 0
0 0 2 0 0 0 0
0 0 0 14 0 0 0
0 0 0 0 1 0 0
0 0 0 0 0 8 0
0 0 0 0 0 0 46

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