# Latex Code for two parallel arrows and alignment in commutative diagram

 && P\times_{\mathcal{H}_0}Q\ar[rdd]\ar[ldd]\\
\mathcal{G}_1\ar[dd] &&\mathcal{H}_1\ar[dd]&&\mathcal{K}_1\ar[dd]\\
&P\ar[dl]\ar[dr]&&Q\ar[dl]\ar[dr]\\
\mathcal{G}_0&&\mathcal{H}_0&&\mathcal{K}_0


This is the code I have written in http://presheaf.com/

It shows the below diagram

I need help in drawing two arrows (just like \rightrightarrows) from script G, H and K.

I also want the square {P\times Q, P, Q, \mathcal{H}_0} to look like a pull back diagram.

Any help is welcome.

• – Zarko Jun 30 '18 at 6:32
• i took a liberty and change title of your question. "double arrow" to much remain people on arrows with double lines ... of course, you can revert my correction. – Zarko Jun 30 '18 at 6:46
• @Zarko thanks for the edit... English is not my native language so could not think of a better word.. thanks again. :) – Praphulla Koushik Jun 30 '18 at 9:04

# Update

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
& & P\times_{\mathcal{H}_0}Q\ar[rd]\ar[ld] & \\[2em]
\mathcal{G}_1\ar[d,shift left]\ar[d,shift right]
& P\ar[dl]\ar[dr]
& \mathcal{H}_1\ar[d,shift left]\ar[d,shift right]
& Q\ar[dl]\ar[dr]
& \mathcal{K}_1\ar[d,shift left]\ar[d,shift right] \\[2em]
\mathcal{G}_0 & & \mathcal{H}_0 & & \mathcal{K}_0
\end{tikzcd}
\end{document}


# Output

Like this?

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
& & P\times_{\mathcal{H}_0}Q\ar[rd]\ar[ld] & \\[2em]
\mathcal{G}_1\ar[d,Rightarrow] & P\ar[dl]\ar[dr] & \mathcal{H}_1\ar[d,Rightarrow] & Q\ar[dl]\ar[dr] & \mathcal{K}_1\ar[d,Rightarrow] \\[2em]
\mathcal{G}_0 & & \mathcal{H}_0 & & \mathcal{K}_0
\end{tikzcd}
\end{document}


# Output

• This is almost the same as what I want.. I want two arrows from $\mathcal{G}_1$ not like one arrow which means an implication... I do not know how to convey it without writing and I don’t know how to write :D – Praphulla Koushik Jun 30 '18 at 2:37
• @PraphullaKoushik Maybe you could draw a picture by hand? – Ruixi Zhang Jun 30 '18 at 3:26
• @PraphullaKoushik Check my updated solution, :) – Ruixi Zhang Jun 30 '18 at 5:45
• Can you tell one more thing... How could you upload that picture? where did you compile?? I do not know if any compiler would make it easier to take diagram and save as an image.. presheaf.com will compile xypic code and give an image.. did you do like this for tikz from some other website? – Praphulla Koushik Jul 3 '18 at 17:13
• @PraphullaKoushik It’s just a screenshot cropped appropriately. I compiled my code in TeXworks on my PC. To upload a picture, click on the image icon when posting/editing. – Ruixi Zhang Jul 3 '18 at 22:52

With tikzcd you could use xshift and draw 2 arrows side by side with the shifting you like.

\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
& & P\times_{\mathcal{H}_0}Q\ar[rd]\ar[ld] & \\[2em]
\mathcal{G}_1\ar[d, xshift=2pt]\ar[d, xshift=-2pt] & P\ar[dl]\ar[dr] & \mathcal{H}_1\ar[d, xshift=2pt]\ar[d, xshift=-2pt] & Q\ar[dl]\ar[dr] & \mathcal{K}_1\ar[d, xshift=2pt]\ar[d, xshift=-2pt] \\[2em]
\mathcal{G}_0 & & \mathcal{H}_0 & & \mathcal{K}_0
\end{tikzcd}
\end{document}


You can slide an arrow sideways by saying, e.g., \ar@<1ex>[dd] to move it a distance of 1ex or \ar@<-1ex>[dd] to move it the other way a distance of 1ex. Thus, you can get two parallel arrows by using both of those commands, one after the other. For example:

\documentclass[12pt]{amsart}
\usepackage[all,cmtip]{xy}

\begin{document}
\thispagestyle{empty}
\begin{displaymath}
\xymatrix{%
&& P\times_{\mathcal{H}_0}Q\ar[rdd]\ar[ldd]\\
\mathcal{G}_1\ar@<0.5ex>[dd] \ar@<-0.5ex>[dd]
&&\mathcal{H}_1\ar@<0.5ex>[dd] \ar@<-0.5ex>[dd]
&&\mathcal{K}_1 \ar@<0.5ex>[dd] \ar@<-0.5ex>[dd]\\
&P\ar[dl]\ar[dr]
&&Q\ar[dl]\ar[dr]\\
\mathcal{G}_0
&&\mathcal{H}_0
&&\mathcal{K}_0
}
\end{displaymath}
\end{document}


produces

See. e.g., section 8.10 of www-math.mit.edu/~psh/amshelp/2.3/amshelp.pdf

I don't know what you mean about the square looking like a pullback diagram.

• I mean the diagram that is in other two answers :) – Praphulla Koushik Jun 30 '18 at 7:44