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### Graph Creation and Copying

Graphs of all of the various types supported by LINK can be created from the GUI. LINK's main window has an option called Graph Windows explicitly for this purpose. Graph types are selected by proceding through the cascading menus associated with that option. The user's selections provide answers to the three questions listed below, then a window containing a graph of the appropriate type appears.

- graph or hypergraph?
- directed undirected, or mixed?
- multiple edges allowed or not?

It is also possible to redefine the graph associated with a graph view. The File menu has the following menu options to change the graph being viewed or bring up new graph views.

- New This option brings up the same cascade of menus used in creating graphs from the main window. The user selects a graph type, and a new empty graph of the appropriate type replaces the the current graph (which is lost).
- Generate It is often desirable to call algorithms which generate graphs rather than creating graphs by hand. The Generate menu current supports the generation of cycles, complete graphs, grids, and uniform hypergraphs, but adding new generators is straightforward (though as yet undocumented 7/19/96).
- Clone Often one wants to compare a slight variation of a graph G with G itself. The Clone option will bring up an exact copy of a graph, which can then be modified without affecting the original.
- Multi-Graph Clone All graphs in LINK either allow multiple edges or do not. In certain cases, such a collapsing groups of vertices into subgraphs, it is necessary to allow multiple edges. If such an operation is needed for a simple graph, this option will bring up a clone of the graph, except of the corresponding type allowing multiple edges.
- Simple Graph Clone Similar to Multi-Graph Clone, except that the new copy of the graph is always a simple graph.

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