3
 && 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

enter image description here

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
  • 296,517
Praphulla Koushik
  • 304
  • see https://tex.stackexchange.com/questions/433615/ – Zarko Jun 30 '18 at 06:32
  • 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 06:46
  • @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 09:04

3 Answers3

5

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}

enter image description here

CarLaTeX
  • 62,716
4

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

enter image description here

Original answer

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

enter image description here

Ruixi Zhang
  • 9,553
  • 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 02:37
  • @PraphullaKoushik Maybe you could draw a picture by hand? – Ruixi Zhang Jun 30 '18 at 03:26
  • @PraphullaKoushik Check my updated solution, :) – Ruixi Zhang Jun 30 '18 at 05:45
  • 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.. http://presheaf.com/ will compile xypic code and give an image.. did you do like this for tikz from some other website? – Praphulla Koushik Jul 03 '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 03 '18 at 22:52
3

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

enter image description here

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.

Phil Hirschhorn
  • 8,942