[igraph] Some peculiarities

[Jukka Ruohonen]

Hello.

I have two simple and possibly stupid questions. 

First, consider the following R snippet:

        p <- function(y) {
          g <- graph.adjacency(y, mode = "directed");
          plot(g, layout = layout.spring);
        }
 
        par(mfrow=c(3, 1));

        x <- matrix(0, nrow = 3, ncol = 3);
        x[3, 2] <- 1; p(x); x[2, 3] <- 1;

        p(x);
        p(x); # Output differs.

Why does the output differ between the last two calls to p()?

Second, I wonder whether there is a simple explanation why triad.census()
may return negative values for empty subgraphs? This is with a large
real-world directed dataset; I didn't find an easy way to reproduce or
demonstrate this.

- Jukka.