graphics, grDevices, igraph, network, sna, stats
knitr, rmarkdown, markdown, igraphdata, intergraph, ggraph,
gridGraphics, ggplot2, gridExtra, gridBase, magrittr
knitr, rmarkdown, markdown, igraphdata, intergraph, ggraph,
gridGraphics, ggplot2, gridExtra, gridBase, magrittr, tinytest