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I frequently tried to draw a triangle commutative diagram similar to the definition of projective modules for this question.

A module associated to an endomorphism of a vector bundle

so I searched in latex stackexchange and I find some relevant post.

then I copy paste the corresponding commands and I observed that that does not work for MO.

I copied the commands in this post:

https://tex.stackexchange.com/questions/191462/creating-triangle-commutative-diagram-with-tikz-cd

(I prefer $\gamma$ lies on a Dots arrows.

can I ask you to kindly help me to draw this diagram. such a diagram can present my meaning more precisely.

thank you in advance for your help.

P.S.: Even when I try a simple command as $$\begin{CD} A \\ @VVV \\ B \end{CD}$$

It does not work at MO.

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This is a community wiki answer made explicitly for testing.

$$\require{AMScd}\begin{CD}
A \\
@VVV \\
B
\end{CD}$$

$$\require{AMScd}\begin{CD} A \\ @VVV \\ B \end{CD}$$

$$\require{AMScd}
\def\diaguparrow#1{\smash{
  \raise.6em\rlap{\scriptstyle #1}
  \lower.3em{\mathord{\diagup}}
  \raise.52em{\!\mathord{\nearrow}}
}}
\begin{CD}
&& E\\
& \diaguparrow{\gamma} @VV \alpha V \\
F @>> \beta> G
\end{CD}$$

$$\require{AMScd} \def\diaguparrow#1{\smash{ \raise.6em\rlap{\scriptstyle #1} \lower.3em{\mathord{\diagup}} \raise.52em{\!\mathord{\nearrow}} }} \begin{CD} && E\\ & \diaguparrow{\gamma} @VV \alpha V \\ F @>> \beta> G \end{CD}$$ This comes from taking the three characters $\gamma \diagup \nearrow$, adjusting their heights, using rlap so that the first two characters overlap, using $\backslash !$ to back up the third character, using smash to make them all spill out of a $0\times 0$ box, and then putting that box in the right place.

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  • 1
    $\begingroup$ Thank you very much for your answer. I applied your help. But can you say me how can I replace the inclined arrows by a Doted one? $\endgroup$ – Ali Taghavi Jan 16 at 12:21
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    $\begingroup$ @AliTaghavi I do not know about a way to make the diagonal arrow dotted using AMScd. I have asked Davide Cervone (one of MathJax developers) in the comments to his answer, he does not mention a way to do this either. $\endgroup$ – Martin Sleziak Jan 17 at 1:54
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Especially for more complicated diagrams (where it's difficult to draw them using AMScd), a possible solution is to use presheaf website and include the picture into the post. I have learned about this site from Bruno Stonek's answer to How to draw a commutative diagram? (Mathematics Meta).

Advantages of this website:

  • It is easy to use for people who are already familiar with xypic. (Of course there are also other LaTeX packages for commutative diagrams, the most popular probably are tikz-cd and xy-pic.)
  • The code is compiled online and it generates picture which can be used elsewhere. (Naturally, some users might prefer to do this locally on their computer and convert the output from LaTeX to picture by themselves.)
  • If you add link to the website, you simultaneously provide the xypic code.

I will explicitly mention that images uploaded through the editor should be stable and relatively immune to link rot, see: Permanent Picture Uploads (Mathematics Meta).

I am fully aware that this is not optimal from the viewpoint of screen readers and visually impaired users. However, web accessibility is probably quite a challenging issue when using commutative diagrams and various other visualizations.

Some examples:

http://presheaf.com/?d=d5f3h332d491j3m2v5j4g5o193hr503v

{\hat P} \ar[rd]^k \ar[rrd]^{\hat f} \ar[rdd]_{\hat g} \   & P \ar[r]_{\overline  f} \ar[d]^{\overline g} & B \ar[d]^g \   & A \ar[r]_f & C

http://presheaf.com/?d=d564x6z6o2c383r6t3r55r375c4v4l1h

& E \ar[d]_\alpha \ E \ar@{..>}[ru]^\gamma \ar[r]_\beta & E

http://presheaf.com/?d=d4l86n4i40s4n18675m3rw6cye1p

{X} \ar@{^{(}->}[r] \ar[rd]_f  & {\beta X} \ar[d]^{\widehat f} \ & {K}

http://presheaf.com/?d=d6213453at1p2gd324i21h3i4g3v32

B \ar[r]^{r_B} \ar[rd]_{f}& {A_B} \ar@{-->}[d]^{\overline f} \ & A

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