Creating triangle commutative diagram with tikz-cd [duplicate]

Question

I've just started using TikZ and need to create a simple triangle commutative diagram like this one.

The closest I've been able to get is this.

How do I get the h arrow to go from A2 to A3? Everything I've tried just causes errors.

Here's my current code:

\begin{tikzcd}[column sep=small]
A \arrow{r}{i}  \arrow{rd}{g} 
  & A3 \arrow{d}{h} \\
    & A2
\end{tikzcd}

Answer 1

Update

A better syntax has evolved with time, which has several advantages due to improvements in TikZ and is now recommended.

\documentclass{article}
\usepackage{tikz-cd}

\begin{document}

\[
\begin{tikzcd}
 & A \arrow[dr,"g"] \\
B \arrow[ur,"f"] \arrow[rr,"h"] && C
\end{tikzcd}
\]
\[
\begin{tikzcd}[row sep=2.5em]
 & A \arrow[dr,"g"] \\
B \arrow[ur,"f"] \arrow[rr,"h"] && C
\end{tikzcd}
\]
\[
\begin{tikzcd}[column sep=1.5em]
 & A \arrow[dr,"g"] \\
B \arrow[ur,"f"] \arrow[rr,"h"] && C
\end{tikzcd}
\]
\end{document}

Original answer

The basic idea for triangular diagrams is to consider more columns, in this case three; you may want to play with column sep or row sep in order to get better distances, as shown.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\[
\begin{tikzcd}
 & A \arrow{dr}{g} \\
B \arrow{ur}{f} \arrow{rr}{h} && C
\end{tikzcd}
\]
\[
\begin{tikzcd}[row sep=2.5em]
 & A \arrow{dr}{g} \\
B \arrow{ur}{f} \arrow{rr}{h} && C
\end{tikzcd}
\]
\[
\begin{tikzcd}[column sep=1.5em]
 & A \arrow{dr}{g} \\
B \arrow{ur}{f} \arrow{rr}{h} && C
\end{tikzcd}
\]
\end{document}

---

If you want to try this with QTikZ, you need a suitable template; create the text file tikz-cd-template.pgs with

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
<>
\end{document}

Choose the template and then paste the part of the above code which is between \begin{document} and \end{document} in the input window for QTikZ. Here's a picture of the result.

If you have an old version of tikz-cd (which might be the case on Ubuntu or other GNU/Linux boxes) it may be necessary to start the diagram with {}:

\[
\begin{tikzcd}
{} & A \arrow{dr}{g} \\
B \arrow{ur}{f} \arrow{rr}{h} && C
\end{tikzcd}
\]