How to best deal with ordering of multiple wires?

[JonathanGitGood]

I am having trouble with drawing nice diagrams once there are many wires. I am trying to TeX the ZX spider fusion rule, but I can't get it to look nice. I either have crossing wires or they might be too close to each other, like in my current best attempt:

\begin{align*}
\begin{ZX}[
    /utils/exec={
        \def\Zalpha{
            \zxZ{\alpha}\ar[to=beta,(,start anchor=south, end anchor=north]
            \ar[to=beta, 3 vdots]\ar[to=beta,), start anchor=south, end anchor=north]
        }
        \def\Zbeta{
            \zxZ[a=beta]{\beta}
        }
    }
]
\leftManyDots{} \Zalpha \rightManyDots{} & \\
\\
        & \leftManyDots{} \Zbeta \rightManyDots{}
\end{ZX}
\end{align*}

Whilst the anchors prevent any crossing over, it makes it look very ugly. Furthermore, it makes the readability of the middle vdots worse. Lastly, I don't like how the ManyDots get lengthened on one side and not on the other. Help would be greatly appreciated!

[tobiasBora]

I can't test right now as I don't have my computer with me, but are you aware that you can fine-tune the width and height of each column and line with &[2mm] and \\[2mm], including with negative parameters (or even presets for homogenius value across code)? It can sometimes help you to have nicer looking pictures. You can also write your own code for ManyDots, the actual code is not complicated and can easily be adapted to your own settings, just search for ManyDots in the source code, the default code work mostly in simple settings. In complex settings, you can also use regular tikz styles for arrows, like out=0,in=100,s=1.5 or the more low-level bezier style provided in this lib.

Also, in my experience I find diagrams made with diagonal lines + dots quite crowded so I often prefer to stack them horizontally or vertically, see for instance p28 of https://arxiv.org/pdf/2402.01445 or p32 of https://leo.colisson.me/articles/2022_-_PhD/PhD_Leo_Colisson.pdf.

[JonathanGitGood]

Thank you very much for the quick reply and all the pointers!
I have tried changing the column width, but it seems to get mostly overwritten by the size of the alpha and beta nodes, thus stretching the wires in the column above and below.
Is there an option to make an invisible node that behaves like the Z and X spiders? The zxN{} nodes only attach in very limited ways when I play around with out=0,in=100,s=1.5 as you have suggested. And they don't stretch the wires in the same way.

Sadly, I don't find stacking them as visually pleasing, and would much prefer having them placed diagonally.

[tobiasBora]

Ok, in this specific example, to stretch columns you need to unfold the definition of \rightManyDots as the columns are actually defined here, or add an empty column above as the size must be written above the first column. But I think I managed to get a nice version without changing any of these by using:

• angle anchors to specify a more precise anchor, e.g. at -40° instead of south
• invisible nodes to have even spacing (this also answers your question) via \zxX[opacity=0]{\alpha}

This way I can get:

via

\documentclass[]{article}
\usepackage{amsmath}
\usepackage{zx-calculus}

\begin{document}
\begin{align*}
\begin{ZX}[
    /utils/exec={
        \def\Zalpha{
            \zxZ{\alpha}\ar[to=beta,(,start anchor=south, end anchor=180-40]
            \ar[to=beta, 3 vdots]\ar[to=beta,), start anchor=-40, end anchor=90]
        }
        \def\Zbeta{
            \zxZ[a=beta]{\beta}
        }
    }
]
\leftManyDots{} \Zalpha \rightManyDots{} & \zxX[opacity=0]{\alpha} \\[3mm]
\zxX[opacity=0]{\alpha}                 & \leftManyDots{} \Zbeta \rightManyDots{} 
\end{ZX}
\end{align*}
\end{document}

Hope you like it, if not let me know how we can improve it.

[JonathanGitGood]

Wow, thank you very much! This is great, and the lesson provided will help a lot with future diagrams, too.