. . . okay, I realize that a viable Latex document has many preliminary
commands. Here's a "working" version of my tangled code

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{trees}
\begin{document}

\begin{tikzpicture}
  \node [circle, draw, fill=red!20] at (0,0) {1}
  child { node [circle, draw, fill=blue!30] {2}
    child { node [circle, draw, fill=green!30] {3} }
    child { node [circle, draw, fill=yellow!30] {4} }};
\end{tikzpicture}
\end{document}

I guess I need to know where to begin to get the "default" org-mode Latex
export functionality for Latex babel tangling.

But then maybe I'm barking up the wrong tree. One of the hardest things
about learning org-mode is finding out what the "best practice" of
something really is.

On Sun, Apr 26, 2015 at 7:20 PM, Lawrence Bottorff <borgauf@gmail.com>
wrote:

> I'm following the Latex howto of org-mode babel. Here's the snippet from
> the howto I've got in a separate .org file (see bottom of howto page):
>
> #+LATEX_HEADER: \usepackage{tikz}
>
> First execute the second code block, to define the convenience macro
> and to set the required new variables in ob-latex.el.  Then export to
> HTML and to pdf to see the tree exported as an SVG image and as
> embedded tikz respectively.
>
> * Tikz test
> Here's a tree, exported to both html and pdf.
>
> #+header: :file (by-backend (html "tree.svg") (t 'nil))
> #+header: :imagemagick
> #+header: :results (by-backend (pdf "latex") (t "raw"))
> #+header: :tangle yes
> #+begin_src latex
>   \usetikzlibrary{trees}
>   \begin{tikzpicture}
>     \node [circle, draw, fill=red!20] at (0,0) {1}
>     child { node [circle, draw, fill=blue!30] {2}
>       child { node [circle, draw, fill=green!30] {3} }
>       child { node [circle, draw, fill=yellow!30] {4} }};
>   \end{tikzpicture}
> #+end_src
>
> * COMMENT setup
> #+header: :tangle yes
> #+begin_src emacs-lisp :results silent
>   (setq org-babel-latex-htlatex "htlatex")
>   (defmacro by-backend (&rest body)
>     `(case (if (boundp 'backend) (org-export-backend-name backend) nil)
> ,@body))
> #+end_src
>
> This doesn't really produce a .svg of the tree as advertised, but
> exporting to Latex does produce it just fine.
>
> My real confusion starts when I try to tangle the babel code blocks. The
> C-c C-v t command produces two separate files just fine, a .tex and .el,
> but then if I try to Run Latex on the .tex file just by itself it gives an
> error. Here's what the org-mode tangle produces:
>
> \usetikzlibrary{trees}
> \begin{tikzpicture}
>   \node [circle, draw, fill=red!20] at (0,0) {1}
>   child { node [circle, draw, fill=blue!30] {2}
>     child { node [circle, draw, fill=green!30] {3} }
>     child { node [circle, draw, fill=yellow!30] {4} }};
> \end{tikzpicture}
>
> And here's the error log after I try to run it by itself in Emacs:
>
> . . .entering extended mode
>  restricted \write18 enabled.
>  file:line:error style messages enabled.
>  %&-line parsing enabled.
> **\input prac2.tex
> (./prac2.tex
> ./prac2.tex:2: Undefined control sequence.
> l.2 \usetikzlibrary
>                    {trees}
> The control sequence at the end of the top line
> of your error message was never \def'ed. If you have
> misspelled it (e.g., `\hobx'), type `I' and the correct
> spelling (e.g., `I\hbox'). Otherwise just continue,
> and I'll forget about whatever was undefined.
> Another version (from C-c `) produces this error message:
>
> ERROR: Undefined control sequence.
>
> --- TeX said ---
> l.2 \usetikzlibrary
>                    {trees}
> --- HELP ---
> TeX encountered an unknown command name. You probably misspelled the
> name. If this message occurs when a LaTeX command is being processed,
> the command is probably in the wrong place---for example, the error
> can be produced by an \item command that's not inside a list-making
> environment. The error can also be caused by a missing \documentclass
> command.
>
> What am I missing here? I'd like to be able to keep my org stuff separate
> from the Latex source, which org-mode seems to do nicely. But then it has
> to run properly too. . . .
>
> LB
>