[igraph] help with gadget replacement

[Raphael C]

I quite often need to replace nodes with little graphs as gadgets and
I haven't quite got used to how to do this in igraph (python). In this
case this is the rule.

Assume the graph is directed and weighted with positive weights.  For
every node X with outdegree > 1, here is an example to demonstrate
what I would like to do.

Assume we have incoming edges

A->X with weight x1
B->X with weight x2

and outgoing edges

X->D with weight x3
X->E with weight x4
X->F with weight x5

I would like to replace X with three nodes (the same as the outdegree)

X1->D with weight x3
X2->E with weight x4-1
X3->F with weight x5-2

and connect A and B to X1 with the same weight they had before when
connected to X

and add X1->X2 with weight 1 and X2->X3 with weight 1.

The end result should be that all nodes have outdegree at most 1 and
all paths between "1" versions of nodes should have the same cost as
they had before.


Any help very much appreciated.

Raphael