I am trying to use Laplacian Solvers to solve a linear equation. I am just learning it (form here), so my question is very basic and it might not even make sense.

Suppose that we want to solve Ax=b, where matrix A is not a Laplacian matrix. Under what condition on A and b, we can solve Ax=b using Laplacian solvers?

P.S. Introducing a good reference will be helpful too.

  • $\begingroup$ Please don't simultaneously cross-post. $\endgroup$
    – D.W.
    Feb 20, 2021 at 6:13

1 Answer 1


It's a good question. You can use a Laplacian solver if $A$ is symmetric and diagonally semi-dominant (SDD). This is the subject of Theorem 9.2 in your reference book from Vishnoi. A good exposition of the proof (which was originally by Gremban) can be found in Appendix A of the paper by Kelner, Orecchia, Sidford and Zhu (arXiv:1301.6628).

A recent result by Kyng and Zhang (arXiv:1705.02944) suggests that current Laplacian solvers are probably restricted to this class.

  • $\begingroup$ Thanks a lot. Your answer and the references are really helpful. $\endgroup$
    – Mah
    Feb 20, 2021 at 15:23
  • $\begingroup$ Unfortunately the matrix $A$ in my equation is not SDD, but it is sparse. Is there any other approach that I can use to solve it fast? $\endgroup$
    – Mah
    Feb 20, 2021 at 15:28
  • 1
    $\begingroup$ For general sparse matrices you can do slightly better. See e.g. arXiv:2007.10254 and references therein. $\endgroup$
    – smapers
    Feb 21, 2021 at 14:20
  • $\begingroup$ Great! This is exactly what I was looking for. $\endgroup$
    – Mah
    Feb 21, 2021 at 17:25

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