Creating triangular matrix from a vector (with a twist)

I have a vector v=[a b c d] and I want to (efficiently) create a matrix of the form : M=[a 0 0 0 ; b a 0 0 ; c b a 0 ; d c b a ]. I am experimenting with "diag" function but it does not seem to be very efficient. Any thoughts?

Answer 1

[Matt J]

>> toeplitz([1 2 3 4],[1,0,0,0])

ans =

       1     0     0     0
       2     1     0     0
       3     2     1     0
       4     3     2     1