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*To*: Beng-Hong Lim <jsp@yktvmh.bitnet>*Subject*: 1displaying graphs0*From*: "J. Scott Penberthy" <JSP@ibm.com>*Date*: Thu, 8 Oct 87 19:07 EDT*Character-type-mappings*: (1 0 (NIL 0) (:SWISS NIL NIL) "HL12")*Courier-to*: BHLIM%JASPER@LIVE-OAK.LCS.MIT.EDU, slug@r20.utexas.edu*Fonts*: CPTFONT, HL12*In-reply-to*: <871008134857.3.BHLIM@PENANG.Palladian.COM>*Resent-date*: Thu 8 Oct 87 20:27:57-CDT*Resent-from*: CMP.SLUG@r20.utexas.edu*Resent-message-id*: <12340969100.30.CMP.SLUG@R20.UTEXAS.EDU>*Resent-to*: SLUG:;

Beng-Hong, I've got a graph Browser that let's someone peruse a directed graph; its got a 2d, reshapeable cursor so that you can control both (1) the number of nodes seen in a window, and (2) the portion of the graph seen in a window. This browser also allows you to (optionally) specify how the nodes should appear (i.e. their shape + their contents). I use a simple layout routine that draws all graphs in a tree format. Cycles within the graph are handled by either duplicating a node that starts a cycle, or by drawing lines across the tree structure. Although I can't distribute my software (IBM's rules), Gabe Robins at ISI devised a similar browser that he sells for about $150. His browser is called the "ISI Grapher," and it uses the same algorithm that I use. I'm sorry that I can't include the algorithm here -- Gabe, on the other hand, details the algorithm on pages 24 and 25 of the ISI Grapher manual. You can obtain the manual by writing to Gabe at Gabriel Robins Information Sciences Institute The Intelligent Systems Division 4676 Admiralty Way Marina Del Rey, California 90292-6695 In your letter you also said that you wanted an algorithm that "should strive to minimize edge crossings and edge lengths and also handle manhattan routing." Such an "optimal layout" algorithm for an arbitrary graph would probably take much more power than the Symbolics can offer. You might have better luck devising a special-purpose algorithm for your own directed graphs; most layout routines take advantage of some aspect of the underlying graph structure. For example, I chose a tree layout since my graphs have few cycles; that may or may not be useful to you. If you have a highly interconnected graph, you might want to contact the VLSI group at MIT and ask them about their layout algorithms. Good luck! Cheers, Scott

**References**:**displaying graphs***From:*Beng-Hong Lim <BHLim@jasper.palladian.com>

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