LyX ⇒ Problems creating a graph (graph theory)

[usr]

Hi,

I wanted to create a graph (with some nodes and edges), xy-pic can do so. The xy-pic-documentation explains in chapter 3.2 how to do so: You create for example a 3*3-matrix with a U-node in the first column/first row and a Y-node in the 3rd row/2nd column. If you want to make an arrow from U to Y write down

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U\ar[ddr]

instead of only

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U

in the first column/first row(that means: "start an arrow at U which ends two times down and one on the right, therefore [ddr]" (where the Y is written).

But if I put the cursor somewhere else there is a problem. Instead of the arrow from U to Y I see U-!Ch!Ch!>[ddr] on the left and top of the matrix.

The strange thing is that I only reproduced the given example but it doesn't work when I write it down by myself. What has happened here?

Thanks!
usr
(Lyx 1.6.9)

[d60pmp]

Perhaps this is unhelpful, but try Graphviz.
http://en.wikipedia.org/wiki/Graphviz

[usr]

Thanks.

I would prefer a lyx-tool so that I can see the graph before I make the PDF. But if that is not possible, I will try that.

Has anyone an idea about the problem with xy-pic. Can you reproduce that problem?

Thanks!
usr

[usr]

Now I think I got it.

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\xymatrix{U\ar@{{-}}[ddr]\\&XY&X\\&Y&Z}

is the code to solve the problem.

I think I made a mistake:
When lyx wants to create graphs you have to create a special matrix before (with

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\xymatrix

) and not those who are created when you take the matrix button (which creates a matrix type called "array"). To see the difference watch the source code.

So you can solve the problem when you type the code at first as written above and then put it into the mathematics mode. (I still don't really understand how to navigate between those xy-matrix elements so I prefer to code all at once and then take the mathematics mode.)

The option

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{{-}}

in the above code has the effect that the arcs are shown as undirected edges.

Thank you!

[d60pmp]

Yep, was just about to post saying the same thing:

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%WORKS
$\xymatrix{A\ar[dr] & B\\
C & D}$

%DOESN'T WORK
$\begin{array}{cc}
A\ar[dr] & B\\
C & D\end{array}$

If you need more detail check out Help -> Specific Manuals -> XY-pic Manual

It's a nice package, I'll probably be using it to draw some more LaTeXy neural networks for my dissertation.

Edit: I'd say that was problem solved, don't forget to stick a tick on the icon.