[igraph] Could not find function "is" in graph.adjacency

[Daigu]

I'm a new R/igraph user. While trying out the example from
http://www.ats.ucla.edu/stat/r/faq/snplot.htm I receive the error "could
not find function 'is'" after executing the graph.adjacency function.

Now when I look at the code for graph.adjacency, I see:

if (is(adjmatrix, "Matrix")) {

Since I have little experience with R I can not be sure, but shouldn't
this be:

if (is.matrix(adjmatrix)) {

I've looked for this in the bug lists but it was not mentioned... rather
doubting it's a bug, but don't have a clue otherwise. Hope you guys can
help me.

See below for my sessionInfo.

R version 2.12.1 (2010-12-16)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] splines   graphics  stats     utils     grDevices tcltk
base     

other attached packages:
[1] Rcmdr_1.6-2     car_2.0-7       igraph_0.5.5-4  survival_2.36-2
[5] nnet_7.3-1      MASS_7.3-9     

Also, library() reports:

Packages in library '/home/daigu/R/x86_64-pc-linux-gnu-library/2.12':

igraph                  Network analysis and visualization
...


Should the package perhaps be in another location?