Creating a diagonal matrix

I will like to create such diagonal matrix. A=[1 1 1 0 0 0; 0 1 1 1 0 0; 0 0 1 1 1 0; 0 0 0 1 1 1] Appreciate your kind assitance.

Answer 1

[Matt J]

A=conv2(eye(4),[1,1,1])

[Andrei Bobrov]

+1

Answer 2

[John D'Errico]

That is not a diagonal matrix, not by the common definition of the term. It has non-zero diagonals, but that is as far as I might go.

Still trivial though.

triu(tril(ones(4,6),2))
ans =
   1     1     1     0     0     0
   0     1     1     1     0     0
   0     0     1     1     1     0
   0     0     0     1     1     1

Or...

toeplitz([1 0 0 0]',[1 1 1 0 0 0])
ans =
   1     1     1     0     0     0
   0     1     1     1     0     0
   0     0     1     1     1     0
   0     0     0     1     1     1

Answer 3

[Andrei Bobrov]

full(spdiags(ones(4,3),0:2,4,6))

or

t = true(4,6);
out = tril(t,2) & triu(t)

or

a = triu(ones(4,3));
out = [a,rot90(a,2)]

Answer 4

[Matt J]

You could also use interpMatrix ( Download ) in a somewhat weird way,

A=full( interpMatrix( [1,1,1] , 1,4,1,'allcontrib') )