How to plot a tree/graph/web with weighted edges in Gnuplot?

Question

i am plotting a tree in gnuplot as discussed here (How to plot tree/graph/web data on gnuplot?). However, i would like to include the edges weight of the tree, i.e. for each edge i have a number (e.g. 10, 20, 30, 40) that represents the edge weight. The figure below shows in red the edges weight that i want to plot in gnuplot (i added this using power point).

Can anyone tell me how to plot edges with weight in gnuplot?

Answer 1

I would propose a slight variation on the answer which you mention in your question. Let's assume that the coordinates of the vertices are stored in a file pnts.dat as follows:

0   5   10
1   20  20
2   15  15
3   30  30
4   40  10

Here, the first column records the corresponding label, while second and third columns contain the x- and y-coordinate, respectively.

The edges could be defined in a separate file edges.dat as:

0   1   30  0   1
1   2   40  0   -2
1   4   20  0   1
1   3   10  0   1

Here, the first two column contain the point indices (they refer to the first column of pnts.dat). The third column records the weight of a particular edge. Finally, the last two columns contain the x,y displacement of the generated associated label.

With this, the Gnuplot script could look like:

set xr [0:50]   
set yr [0:50]

set size square   

flePnts = 'pnts.dat'
fleEdges = 'edges.dat'

loadEdges = sprintf('< gawk '' \
    FNR==NR{x[$1]=$2;y[$1]=$3;next;} \
    {printf "%%f\t%%f\n%%f\t%%f\n\n", x[$1], y[$1], x[$2], y[$2];} \
'' %s %s', flePnts, fleEdges); 

loadWeights = sprintf('< gawk '' \
    FNR==NR{x[$1]=$2;y[$1]=$3;next;} \
    {printf "%%f\t%%f\t%%s\n", (x[$1]+x[$2])/2 + $4, (y[$1]+y[$2])/2 + $5, $3} \
'' %s %s', flePnts, fleEdges);

plot \
    loadEdges using 1:2 with lines lc rgb "black" lw 2 notitle, \
    flePnts using 2:3:(0.6) with circles fill solid lc rgb "black" notitle, \
    flePnts using 2:3:1 with labels tc rgb "white" font "Arial Bold" notitle, \
    loadWeights using 1:2:3 with labels tc rgb "red" center font "Arial Bold" notitle

1. the loadEdges command invokes gawk in order to generate for all edges the corresponding pairs of x/y coordinates (delimited by a blank line)
2. loadWeights calculates for each edge the middle point and places a label at these coordinates (taking into account the required offset)

Finally, one obtains: