Scilab function

arc_graph - graph with nodes corresponding to arcs

### Calling Sequence

  `g1 = arc_graph(g)`

### Parameters

- `g` : graph list of the old graph
- `g1` : graph list of the new graph

### Description

`arc_graph` returns the directed graph `g1` with the nodes corresponding to the arcs of the directed graph `g`. `g1` is defined in the following way:

- its nodes correspond to the arcs of `g`

- 2 nodes of the new graph are adjacent if and only if the corresponding arcs of the graph `g` are consecutive.

The coordinates of the nodes of `g1` are given by the middle points of the corresponding edges of `g`.

If such an arc graph does not exist, an empty vector is returned.

### Examples

    ta=[1 1 2 4 4 5 6 7 2 3 5 1];
    he=[2 6 3 6 7 8 8 8 4 7 3 5];
    g=make_graph('foo',1,8,ta,he);
    g('node_x')=[281  284  360  185  405  182  118  45];
    g('node_y')=[262  179  130  154  368  248  64  309];
    show_graph(g);
    g1=arc_graph(g);
    show_graph(g1,'new');

### See Also

`line_graph`