[igraph] tkplot() - error message

[Diana Neufeld]

Dear all,

I have a question to the function:  tkplot().

My graph has following properties:

>  print(graph)
Vertices: 51 
Edges: 463 
Directed: TRUE

If I use the following command:

> tkplot(graph , layout=pub.mat)

I get the error message:

Error in structure(.External("dotTclObjv", objv, PACKAGE = "tcltk"), class = 
"tclObj") : 
  [tcl] bad screen distance "-pubMedID".

pub.mat  is a matrix with two columns like this:

   pubMedID ArticleDate
12    53631           11
15   475066          14
16   517816          15
14   637382          13
13   744792          12
27  1415150         26
…

Without the argument layout in the function tkplot() it works. 
Whit   plot.igraph(graph, layout=pub.mat)     it also works. But I need an 
interactive graphic.
What does the error message mean? Where is the problem?

regards, di

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