[R-SIG-Mac] Problem viewing silhouette plot in Adobe Acrobat

[Retzer Joe]

I'm having a problem viewing a silhouette plot created as a pdf file  
in Adobe Acrobat.  The code below produces a silhouette plot which,  
when saved as a pdf file, has bars that are not visible in Adobe  
Acrobat. A similar problem was noted earlier in the archives (from  
which I took this code) but for a png file. The archive emails  
suggested it may have been a resolution problem however did not have a  
simple workaround, which I assume may exist.

Note also that the bars of the silhouette plot below are viewable in  
the MAC "preview" app.

      library(cluster)
      nmat <- matrix(rnorm(2500*300), ncol=300, nrow=2500)
      rmat <- matrix(rchisq(1000, 300, 50), ncol=300, nrow=1000)
      mat <- rbind(nmat, rmat)
      pr <- pam(mat, 2)
      plot(silhouette(pr))

Any help would be appreciated,

Many thanks,
Joe Retzer