#*****************************************************************************80
#
## web_digraph plots a web of connections as a directed graph.
#
#  Discussion:
#
#    This Rgraphviz package is stoopid.  It does not want to label
#    edges.  In this example, I have a directed graph with weighted
#    edges.  I want each edge to be labeled by its weight.  But the
#    software fails in one case, where there are two edges between
#    nodes Alpha and Epsilon.  The software can only use one weight
#    as a label.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    06 September 2020
#
#  Author:
#
#    John Burkardt
#
library ( Rgraphviz )

cat ( "\n" )
cat ( "web_digraph:\n" )
cat ( " ", version$version.string, "\n" )
cat ( "  Plot a web of connections as a directed graph.\n" )
#
#  Specify the node labels.
#
nodes <- c ( 'Alpha', 'Beta', 'Gamma', 'Delta', 'Epsilon', 'Zeta' )
#
#  Create the graph.
#
G <- new ( 
  "graphNEL", 
  nodes = nodes, 
  edgemode = "directed" )
#
#  Add edges.
#
G <- addEdge ( "Alpha", "Epsilon", G, weight = 0.1 )
G <- addEdge ( "Alpha", "Zeta", G, weight = 0.9 )

G <- addEdge ( "Beta", "Alpha", G, weight = 0.3 )
G <- addEdge ( "Beta", "Gamma", G, weight = 0.4 )
G <- addEdge ( "Beta", "Delta", G, weight = 0.3 )

G <- addEdge ( "Gamma", "Delta", G, weight = 0.6 )
G <- addEdge ( "Gamma", "Epsilon", G, weight = 0.4 )

G <- addEdge ( "Delta", "Epsilon", G, weight = 1.0 )

G <- addEdge ( "Epsilon", "Alpha", G, weight = 0.2 )
G <- addEdge ( "Epsilon", "Zeta", G, weight = 0.8 )

G <- addEdge ( "Zeta", "Delta", G, weight = 1.0 )
#
#  Idiotic complications to show weights as labels,
#  and it doesn't even work if a pair of nodes shares two edges.
#  Why can't I just add a "label = string" argument to addEdge?
#
ew <- as.character ( unlist ( edgeWeights ( G ) ) )
ew <- ew[setdiff(seq(along=ew), removedEdges(G))]
names(ew) <- edgeNames(G)
eAttrs <- list()
eAttrs$label <- ew
attrs <- list()
attrs$edge$fontsize <- 27
#
#  Make the plot.
#
filename = "web_digraph.png"

png ( filename )

plot ( G, 
  recipEdges = "distinct", 
  edgeAttrs = eAttrs, 
  attrs = attrs,
  main = "web digraph" )

cat ( '  Graphics saved as "', filename, '"\n' )
#
#  Terminate.
#
cat ( "\n" )
cat ( "web_digraph:\n" )
cat ( "  Normal end of execution.\n" )
quit ( )