Re: [igraph] page.rank speed

[Werner Smith]

Tamás Nepusz <address@hidden> writes:



> 

> >  At arpack.c:1178 : ARPACK error, The Schur form computed by LAPACK 
routine dlahqr could not be reordered

> by LAPACK routine dtrsen.

> Seems to be a long-standing issue with ARPACK and we haven't figured out 
yet how to solve this; see, e.g.:

> 

> https://bugs.launchpad.net/igraph/+bug/365817

> https://github.com/igraph/igraph/issues/385

> 

> It seems to occur on relatively sparse graphs and it also seems that 
removing isolated vertices usually

> resolves the problem. Also, the issue will probably not come up again if 
we switch to PRPACK. Can you try

> removing any isolated vertices in your graph (if any) and try again? If 
it still fails, send me your graph

> somehow and I'll investigate.

> 





By any chance, has there been update on this?



I have a single connected graph with:



 decompose.graph(mygraph)

[[1]]

IGRAPH DN-- 133 3497 -- 

+ attr: name (v/c), Weight (e/n)



And I still get issues with ARPACK:



page.rank(mygraph)

Error in page.rank(mygraph) : 

  At arpack.c:1178 : ARPACK error, The Schur form computed by LAPACK 
routine dlahqr could not be reordered by LAPACK routine dtrsen.



So I do not think it is down to isolated vertices, at least not in my case.



Any pointers/hints/tips would be greatly appreciated.



Thank you very much