# Why is HHL the popular choice to solve QLSP and not the Childs et al. (2017) algorithm?

The Childs, Kthari, and Rolando (2017) (CKS) algorithm can solve the quantum linear systems problem (QLSP) in $$\operatorname{poly}(\log N, \log(1/\epsilon))$$ time while the HHL algorithm solves it in $$\operatorname{poly}(\log N, 1/\epsilon)$$ time. So, if the CKS algorithm is superior, then why is the HHL more popular?

Additionally, are there any examples of the CKS algorithm being used to solve a system of equations on a real or simulated quantum computer?

• I suppose only because HHL came earlier and is easier to understand?
– wdc
Mar 26, 2021 at 17:05
• Yea, that makes sense. I was just wondering if there is a technical reason for it. Mar 26, 2021 at 18:24
• I've added the hamiltonian-simulation tag since the CKS algorithm uses it, and people in that field may be interested in providing more insight here in the future. Nov 27, 2021 at 8:57