jgrapht-users — JGraphT user list.

[jgrapht-users] Possible bug & question about GraphDelegator and 'DefaultUndirectedGraph'

[Brecht R. <bre...@gm...>]

Hello all,

I found a possible bug in DefaultEdge (so also in
(Un)Directed(Weighted)Edge) and also in AbstractGraph.containsEdge()
(so also in DefaultDirectedGraph, ...). As I don't have much time to
explain it all, I included my stripped source code, which should be
enough to understand the (possible) bug. Please let me know if my
thoughts are correct.

Besides this, I have two questions:

- I think GraphDelegator should not implement the Graph-interface
(again), since AbstractGraph does already implement Graph, and
GraphDelegator is extending AbstractGraph. Why is GraphDelegator
anyway extending AbstractGraph, and not implementing the
Graph-interface? This doesn't seem logical to me.

- Is there an undirected opposite of the DefaultDirectedGraph?
(something like DefaultUndirectedGraph). I couldn't find it
immediately.

Enjoy the last hours of 2004! :)

cheers,

PS: please include my mail in the (mostly done by doing a 'reply
all'), so I also receive the mail directly, since I'm receiving a
daily digest of this mail.

--
Brecht

[jgrapht-users] Topological order traversal

[Marden N. <mar...@uo...>]

Hi,

I found JGraphT while looking for a nice graph component 
framework which I could plug into the system I am developing.

I need to implement a topological sort to execute a sequence 
of steps with inter-dependencies, forming a directed acyclic 
graph.

I found JGraphT very useful for representing the graph and in 
a few minutes I could adapt the Graph class to an unit test 
of mine (using a dummy DAG and an even simpler adaptor).

But I could not found a topological order traversal in 
JGraphT's distribution. Then I implemented one using the 
excellent infrastructure in the "traverse" package.

There is still some serious unit testing to implement and 
lots of scenarios to validate, but I felt like submitting the 
code to JGraphT's community and get some feedback.

One of the troubles I had when implementing the tests is that 
the topological sort of a DAG is not unique, so it is kind of 
hard to automate the tests. Other thing I could not 
understand clearly is how to defend the code agains cyclic 
graphs.

The code for the TopologicalOrderIterator is attached. If one 
of the committers of the project finds it useful, I would be 
glad to discuss some strategies to implement some unit tests 
for it.

My congratulations to Barak and the others for the good work.

Best regards,
Marden Neubert.=0A =0A___________________________________________________=
_______________________=0AAcabe com aquelas janelinhas que pulam na sua t=
ela.=0AAntiPop-up UOL - =C9 gr=E1tis!=0Ahttp://antipopup.uol.com.br/=0A

[jgrapht-users] future generics support

[Mark N. <mn...@cc...>]

Hello,

I've been using JGraphT for a while, but recently switched over to the 
pre-release Java 1.5, which has support for generics with type 
parameters (like ArrayList<int>).  This makes things a bit nicer as far 
as typing goes, since it enforces at compile time that a container you 
use to hold one type of object actually does holds only that type of 
object (rather than just any 'Object'), and so both avoids run-time 
casting errors, and makes it no longer necessary to cast the objects you 
get out of the container back from 'Object' to their real type.  Are 
there any plans to add this sort of thing to JGraphT, e.g. allowing a 
DirectedGraph<Node>?  I could look at adding it myself when I get some 
free time, as it seems fairly straightforward to do, but I wanted to 
make sure I'm not going to be duplicating something that's already started.

Oh, and thanks for providing a clean and easy-to-use graph library.  
It's incredibly useful---I have no idea why something like this isn't in 
the standard Java libraries, really. =]

-Mark

[jgrapht-users] Mergin two JTrees into a third JTree

[Mindaugas G. <mi...@bp...>]

Hello,

By writing to this mailing list I hoped to get a suggestion on the =
algorithmic problem I have to solve. I have two JTrees, say T1 and T2. I =
have to merge these two trees into the third tree T2 so that it is a =
superset of the first two trees. That is, every node in T1 and T2 is =
represented by some node in the tree T3.

This mailing list has to do with graph theory, thought maybe someone has =
a pseudo-language description of the algorithm like this.

Thank you,

--=20
Mindaugas Genutis
Programmer
No Magic Lithuanian Development Center
Phone: +370 674 05232 Fax: +370 37 320670
e-mail: min...@no...
WWW: http://www.magicdraw.com
--
MagicDraw - UML Made Simple.

[jgrapht-users] JGraphT 0.5.3

[Barak N. <bar...@us...>]

JGraphT version 0.5.3 has been released and is now available to download
from http://jgrapht.sf.net.

Regards,
Barak Naveh

[jgrapht-users] Exporting JGraphT graphs to PNG via JGraph

[Dimitri P. <dim...@gm...>]

Hi!

I'm trying to export a JGraphT-created JGraph to a file using the
following piece of code:

import org.jgraph.pad.GPConverter;
import org.jgraph.pad.GPGraph;
...
GPGraph gpGraph=3Dnull;
BufferedImage img =3D null;
...
gpGraph=3Dnew GPGraph(graph.getModel());
img =3D GPConverter.toImage(gpGraph);
try
{
ImageIO.write(img, "png", new File(selectedFileName));
}
catch (IOException exception)
{
this.logger.error("", exception);
}

graph is a JGraph, which was created from JGraphT.

The code above works fine for JGraphs, which were created without
JGraphT. With JGraphT, it produces an empty (white) PNG image.

How can I export a JGraphT-JGraph to some common image format (PNG or
JPG)?

TIA

dap=20

RE: [jgrapht-users] The code

[Barak N. <bar...@us...>]

Hi Vernon,=20

The problem is in your implementation of class V.

The class overrides the equals() method without overriding hashCode()
method. Doing it is against the contract of equals() and hashCode() =
methods,
and it confuses the HashSet class used internally by JGraphT.

This is a mistake that almost every Java programmer does only once. I'm
saying "once" because it usually takes enough time to find, to never =
forget
about it :).

Please read CAREFULLY the documentation of equals() and hashCode():
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html

The answers are coming ... ;)

All the best,
Barak


> -----Original Message-----
> From: jgr...@li... [mailto:jgrapht-users-
> ad...@li...] On Behalf Of Vernon Smith
> Sent: Thursday, October 23, 2003 02:45
> To: jgr...@li...
> Subject: [jgrapht-users] The code
>=20
>=20
> Hi, Barak,
>=20
> The enclosed is the code for the problems I posted on JGraphT forum. =
The
> class layout is my original approach with a custom Vertex class, which =
is
> not the one in my application, but it yields the same exception. =
Please
> let me know hot to fix the problem.
>=20
> Many thinks.
>=20
> Vernon
>=20

[jgrapht-users] The code

[Vernon S. <vwu...@ly...>]

Hi, Barak,

The enclosed is the code for the problems I posted on JGraphT forum. The class layout is my original approach with a custom Vertex class, which is not the one in my application, but it yields the same exception. Please let me know hot to fix the problem.

Many thinks.

Vernon





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