title: Warning when running cluster_edge_betweenness in R
body: <p>I was trying to do community structure detection based on edge betweenness with igraph package in R. When the edges were weighted, some warning showed up:</p>
  <p>Warning messages:</p>
  <pre><code>1: In cluster_edge_betweenness(g) :
    At community.c:460 :Membership vector will be selected based on the lowest modularity score.
  2: In cluster_edge_betweenness(g) :
    At community.c:467 :Modularity calculation with weighted edge betweenness community detection might not make sense -- modularity treats edge weights as similarities while edge betwenness treats them as distances
  </code></pre>
  <p>When the edges were not weighted, it worked properly without any warning.</p>
  <p>Here's the code for generating the warnings:</p>
  <pre><code>library(igraph)
  g &lt;- make_full_graph(10) %du% make_full_graph(10)
  g &lt;- add_edges(g, c(1,11))
  E(g)$weight &lt;- seq(1,91)
  eb &lt;- cluster_edge_betweenness(g)
  </code></pre>
  <p>I wonder what do the warning messages mean. And should I be concerned?</p>
  <pre><code>Session info:
  R version 3.6.3 (2020-02-29)
  Platform: x86_64-apple-darwin15.6.0 (64-bit)
  Running under: macOS Catalina 10.15.6
  
  Matrix products: default
  BLAS:   /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRblas.0.dylib
  LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib
  
  Random number generation:
   RNG:     Mersenne-Twister 
   Normal:  Inversion 
   Sample:  Rounding 
   
  locale:
  [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] igraph_1.2.6
  
  loaded via a namespace (and not attached):
  [1] compiler_3.6.3  magrittr_1.5    tools_3.6.3     pkgconfig_2.0.3
  </code></pre>