'sym' is an argument to ARPACK, not an option to put in the arpack options
list:

...
baev <- arpack (f2, options=list (n=vcount (g), nev=3, ncv=8, which="LM",
maxiter=200), sym = TRUE
...

The example was wrong before, it is correct now:
http://igraph.org/r/doc/arpack.html

Gabor


On Sun, Feb 23, 2014 at 7:19 AM, Hermann Norpois <[email protected]> wrote:

> Hello,
> I tried the example of arpack{igraph} and I did not make it run with the
> option sym=TRUE
>
>
> g <- erdos.renyi.game (1000, 5/1000)
> M <- get.adjacency (g, sparse=TRUE)
> f2 <- function (x, extra = NULL){cat ("."); as.vector (M %*% x)}
>  baev <- arpack (f2, options=list (n=vcount (g), nev=3, ncv=8, sym = TRUE,
> which="LM", maxiter=200)) # like in the example
> Fehler in arpack(f2, options = list(n = vcount(g), nev = 3, ncv = 8, sym =
> TRUE,  :
>   unkown ARPACK option(s): sym
>
> Without the option sym=TRUE it works but I get a complex vector:
>  baev <- arpack (f2, options=list (n=vcount (g), nev=3, ncv=8, which="LM",
> maxiter=200))
> .............................................................................................................................................................................................................>
>
>  baev$vectors[,1][1:3]
> [1] 0.04375092+0i 0.01087742+0i 0.01028816+0i
>
> complex=FALSE does not work either:
>  baev <- arpack (f2, options=list (n=vcount (g), nev=3, ncv=8, which="LM",
> maxiter=200, complex=FALSE))
> Fehler in arpack(f2, options = list(n = vcount(g), nev = 3, ncv = 8, which
> = "LM",  :
>   unkown ARPACK option(s): complexM <- get.adjacency (g, sparse=TRUE)
>
>
>
> Can you please give me an hint.
> Thanks
> Hermann
>
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>
>
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