With a regular sampling in offset, supposing h0=0, this term becomes:
Consequently, (LLT)ik does not depend only on , and the structure of the matrix LLT is not Toeplitz. So, it is not possible to use Levinson algorithm in the underdetermined transformation , where we have more parameters p than offsets h.
We can reason similarly for the transform . Suppose that, rather than using simply the modeling matrix L, we want to compute the least-squares inverse of LT: (LLT)-1L in the overdetermined case, (LTL)-1LT in the underdetermined case. Thus, Levinson algorithm could only be applied in the underdetermined case.