# Some Arrows in the package tikzcd

Here is the diagram codes and the output of it. I got the codes from the tikzcd documentation but when I want to add some extra arrow, it gives a mistake. How can I add an UP ARROW from "ij-S-open" and a DOWN ARROW from "ij-P-open"?

\begin{tikzcd}[column sep=tiny]
& ij-S-O \ar[dr, Rightarrow] \ar[drr, Rightarrow, bend left=20]
&

&
[1.5em] \\
ij-\alpha-open \ar[ur, Rightarrow] \ar[dr, Rightarrow]
&

&
SP-O \ar[r, dashed]
&
ij-SP-SD \\
&
ij-P-O \ar[ur, Rightarrow]\ar[urr, Rightarrow, bend right=20]
&
&

\end{tikzcd}

• Unrelated: You should replace open with \mathit{open} for proper spacing. Dec 10, 2021 at 20:02
• Thank you so much @SandyG Dec 12, 2021 at 9:30

You need to first create a node to which the arrow can point. The minimal set up for this is {} which depicts an empty node.

Please note that blank lines inside a tikzcd environment will lead to compilation errors. The [1.5em] has no meaning there, hence I removed it.

\documentclass[border=1mm]{standalone}
\usepackage{tikz-cd}

\begin{document}

\begin{tikzcd}[column sep=tiny]
& {} & & \\
& ij-S-O \ar[dr, Rightarrow] \ar[drr, Rightarrow, bend left=20] \ar[u]
&
& \\
ij-\alpha-open \ar[ur, Rightarrow] \ar[dr, Rightarrow]
&
&
SP-O \ar[r, dashed]
&
ij-SP-SD \\
&
ij-P-O \ar[ur, Rightarrow] \ar[urr, Rightarrow, bend right=20] \ar[d]
&
& \\
& {} & &
\end{tikzcd}

\end{document}

• I am afraid of that I will die without learning this package, it is quite hard. Are there any guide book or something which explains easier? @JasperHabicht Dec 10, 2021 at 15:52
• Well, it is essentially a combination of TikZ and array logic. So, you should probably first make yourself comfortable with arrays (but you don't need too much detail here), and then dive into TikZ which has a very nice (but also very large) manual. If you know both good enough, mastering the tikz-cd package is not at all hard. Dec 10, 2021 at 15:56
• thank you so much for the information, I will bring on it @JasperHabicht Dec 10, 2021 at 16:09