Compiling L^{A}T_{E}X to computer algebraenabled HTML5Bernard Parisse 
Abstract: This document explains how to create or modify an existing L^{A}T_{E}X document with commands enabling computations in the HTML5 output: when the reader opens the HTML5 output, he can run a computation in his browser, or modify the command to be executed and run it. This is done by combining different softwares:hevea
[6] for compilation to HTML5,giac.js
for the CAS computing kernel (itself compiled from the C++ Giac[10] library withemscripten
[11]), and a modified version[9] ofitex2MML
[3] for fast and nice rendering in MathML in browsers that support MathML.
Contents
Index
1 Introduction
Combining L^{A}T_{E}X rendering quality and CAS computing is not new:
 math softwares provide converters to export data to a L^{A}T_{E}X file, or provide automated computations in a way similar to the way bibtex provides bibliography, like sagetex ([2]).
 some softwares handle both L^{A}T_{E}Xlike rendering and computation, for example texmacs ([5]), lyx ([7]), Jupyter notebook ([8]).
However, in the first case, the reader can not modify the CAS commandlines, and in the second case the data format is not standard L^{A}T_{E}X (the writer can not start from an existing document) and requires additional software to be installed on the reader device or a net access to a server to run the computations.
The solution presented here is new in that the writer will edit
a standard L^{A}T_{E}X file, add a few easy to learn commands like
\giacinputmath{factor(x^101)}
or \giacinput{plot(sin(x))}
and compile it to produce a HTML5+MathML
document.
The reader can see the document in any browser
(it’s optimized for Firefox), without installation, and he can
modify computation commandlines
and run them on his own computer.
If you are reading this file in PDF format, it is highly recommended to open the HTML5/Mathml version in order to test interactivity and look at the L^{A}T_{E}X source
2 User manual
2.1 Installation on the writer computer
The writer must install
 the latest unstable version of hevea ([6]) or a forked version heveamathjax ([1])),
 Giac/Xcas ([10]) for computingenabled output
 heveatomml ([9]) for MathML output
The files giac.tex (or the French version giacfr.tex) giac.js, hevea.sty, mathjax.sty must be copied in the L^{A}T_{E}X working directory. On an Internet connected linux box, the writer can run once the following shell script to install the tools required for HTML5/MathML output :
#! /bin/bash wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/giac.tex wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/giacfr.tex wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/giac.js wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/hevea.sty wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/mathjax.sty wget http://hevea.inria.fr/distri/unstable/hevea20170518.tar.gz tar xvfz hevea20170518.tar.gz cd hevea20170518 make sudo make install cd .. wget https://wwwfourier.ujfgrenoble.fr/~parisse/giac/heveatomml.tgz tar xvfz heveatomml.tgz cd heveatomml/src make sudo make install cd ../..
2.2 On the writer side
We now assume that the installation is done. The writer opens a L^{A}T_{E}X file with his usual editor. He must add in the preamble the following lines
\makeindex \input{giac.tex} \giacmathjax
For interactive CAS L^{A}T_{E}X commands support, the writer should add
\begin{giacjshere} \tableofcontents \printindex
just after \begin{document}
and
\end{giacjshere}
just before \end{document}
.
Printing the table of contents and index before the first L^{A}T_{E}X
section command is recommended, otherwise the HTML output
Table
and Index
buttons will not link correctly.
The rest of the source file is standard L^{A}T_{E}X except that
 References to numbered equations should be inside additional backslashed parenthesis, for example \begin{equation} \label{eq_test} \frac{2}{x^21}=\frac{1}{x1}\frac{1}{x+1} \end{equation} From equation (\(eq_test\)) ... $\frac{2}{x^21}=\frac{1}{x1}\frac{1}{x+1} \qquad (1)$ From equation (1) ...
\mathbb{}
should be explicit, commands like\R
where\R
is defined by\newcommand{\R}{\mathbb{R}}
will not work. New commands are available for interactive CAS support

\giacinputmath{commandline}
will output an inlinecommandline
that the user can modify and execute, the answer will be displayed in MathML (or SVG for 2d graph output).
Example :\giacinputmath{factor(x^101)}
Warnings, if your command contains<
or>
, you must replace them by<
or>
, otherwise they will be interpreted as HTML delimiters. You can also use thegiacprog
andgiaconload
environments explained below.
If the output is a 2d graph, do not skip a line with\\
after the command for PDF output \giaccmdmath{command}{arguments}
will outputcommand
in a button following thearguments
, the reader can only modify the arguments:
\giaccmdmath{factor}{x^41}
 These commands may take an optional HTML style argument, for example
\giacinputmath[style="width:200px;"]{factor(x^101)}
\giaccmdmath[style="fontsize:xlarge"]{factor}{x^41}
 There are similar commands for outlined output
\giacinputbigmath{}
or\giaccmdbigmath{}{}
:
For example\giacinputbigmath{factor(x^251)}
Example with an optional style argument\giacinputbigmath[style="width:600px;height:20px;"]{factor(x^251)}
\giaccmdbigmath{factor}{x^251}
\giaccmdbigmath[style="width:600px;height:20px;"]{factor}{x^251}
 Similar commands with text (or plot) output
\giacinput
and\giacinputbig
and\giaccmd
, example:
\giacinput{factor(x^41)}
:
\giaccmd{print}{"Hello world"}
:
With optional style argument
\giacinput[style="fontsize:xlarge"]{plot(1/x)}
\giaccmd[style="fontsize:xlarge"]{factor}{x^41}
 The
giacprog
environment should be used for programs or multiline commands
\begin{giacprog}...\end{giacprog}
Inside this environment, you can keep<
and>
. The program will be parsed once the user press theok
button. After parse, the program may be modified and parsed again.
Warning: Do not use thegiacprog
environment in another environment (like itemize or enumerate).
If you want the program to be parsed at loadtime, replacegiacprog
withgiaconload
:
\begin{giaconload}...\end{giaconload}
 The
\giacslider{idname}{min}{max}{step}{value}{command}
command will add a slider. When the user modifies the slider interactively, the newvalue
is stored inidname
and thecommand
(depending onidname
) is executed. Example:
\giacslider{a}{5}{5}{0.1}{0.5}{plot(sin(a*x))}
Not evaled  The
\giachidden
command behaves like\giaccmd
except that the default HTML5 style is “hidden” until the command button has been pressed.  The
\giaclink
command will add a link in the HTML version and nothing in PDF/DVI. The links open in a new tab, and the corresponding text may be specified as optional argument (default is Test online). Note thathevea.sty
provides similar commands (\ahref
,\footahref
,\ahrefurl
) with output in PDF/DVI.
Example with a link to Xcas for Firefox with a few commands
\giaclink{http://wwwfourier.ujfgrenoble.fr/\%7eparisse/xcasen.html#+factor(x^41)&+a:=idn(3)&}
Test online

Once the source file is written, it is compiled to HTML5 with the command
hevea2mml sourcefile.tex
The HTML output and the giac.js
files should be in the same
directory on the web server.
Index and bibliography should be processed with makeindex
and bibhva
.
If a PDF output is desired,
the command icas
from a Giac/Xcas installation
should be used
instead of pdflatex
because it will run all CAS commands, output them in a temporary
L^{A}T_{E}X file,
and run pdflatex
on the output
(this was inspired by the
pgiac script
from JeanMichel Sarlat [4]). The temporary file name
is obtained by adding a _ at the end of the initial file name
(without the .tex extension). Therefore, if you have
an index and or citations, you should run makeindex
and bibtex
on the file name with _
appended. For bibtex
citations in
the HTML files, you should run bibhva
.
For example, the PDF version of this document is available
here.
2.3 On the reader side
The reader’s browser opens an HTML5+MathML file (linking to the JavaScript
giac.js
). The MathML is rendered natively on Firefox or Safari,
while Chrome or Internet Explorer will automatically load MathJax to
render MathML (this is of course noticeably slower if the document is
large).
Computations are run by the reader’s browser (the CAS is JavaScript
code). This is slower than native code but faster than net access to
a server and it does not require setting up a specific server for
computations.
2.4 More examples
2.4.1 Trace (2d graph)
This example illustrates with a slider that the evolute of a curve
is the envelope of the normals to the curve, here the curve is an ellipsis
and the envelop an astroid.
The list of normals L
is initialized empty at loadtime.
L:=[]
onload
Now move the slider:
2.4.2 Cone section (3d graph)
$C$ is a cone of center the origin, axis of direction $(0,0,1)$, and angle $\frac{\pi}{6}$, $P$ is a plane of equation $z=my+3$. $m$ is controlled by the slider, when $m$ moves the intersection is an ellipsis or hyperbola (limit value is a parabola).
2.4.3 Dunford decomposition (CAS)
A program computing the Dunford decomposition
of a matrix with Newton method.
It is parsed at loadtime (giaconload
environment).
function dunford(A) local U,p,q,q1,j,d,n; U:=A; n:=nrows(U); p:=charpoly(U); q:=p/gcd(p,p'); // square free part q1:=q'; for (j:=1;j<=n;j:=2*j){ d:=inv(horner(q1,U))*horner(q,U); // Newton step if (d==0*d) return U,AU; U:=Ud; } return U,AU; end:;
onload
Example : we define $J$ an almost diagonal matrix and $A$ a similar matrix
and we check the Dunford decomposition of $A$.
$J=\left(\begin{array}{ccc}
2 & 0 & 0 \\
0 & 1 & 1 \\
0 & 0 & 1
\end{array}\right) , \quad
P=\left(\begin{array}{ccc}
1 & 0 & 0 \\
2 & 1 & 0 \\
3 & 4 & 1
\end{array}\right), \quad
A=PJP^{1}$
2.4.4 Slopefield
This will display the slopefield of an ordinary differential equation $\frac{dy}{dt}=y+cos(t)$ and one solution corresponding to an initial condition $y(0)$ that the user may modify with the slider.
2.4.5 Gröbner basis (CAS)
The CAS kernel can compute nontrivial Gröbner basis. Of course, the JavaScript version is significantly slower than the native Giac/Xcas kernel.
kat7:=[x1+2*x8^2+2*x7^2+2*x6^2+2*x5^2+2*x4^2+2*x3^2+2*x2^2+x1^2, x2+2*x8*x7+2*x7*x6+2*x6*x5+2*x5*x4+2*x4*x3+2*x3*x2+2*x2*x1, x3+2*x8*x6+2*x7*x5+2*x6*x4+2*x5*x3+2*x4*x2+2*x3*x1+x2^2, x4+2*x8*x5+2*x7*x4+2*x6*x3+2*x5*x2+2*x4*x1+2*x3*x2, x5+2*x8*x4+2*x7*x3+2*x6*x2+2*x5*x1+2*x4*x2+x3^2, x6+2*x8*x3+2*x7*x2+2*x6*x1+2*x5*x2+2*x4*x3, x7+2*x8*x2+2*x7*x1+2*x6*x2+2*x5*x3+x4^2, 1+2*x8+2*x7+2*x6+2*x5+2*x4+2*x3+2*x2+x1]:;
onload
Basis over $\mathbb{Z}/16777213$
3 How this is done
The L^{A}T_{E}X \giac...
commands are defined in giac.tex
.
For example \giacinput
is defined like this:
\newcommand{\giacinput}[2][style="width:400px;fontsize:large"]{ \ifhevea \@print{<textarea onkeypress="UI.ckenter(event,this,1)" } \@getprint{#1>#2} \@print{</textarea><button onclick="previousSibling.style.display='inherit';var tmp=UI.caseval(previousSibling.value);tmp=UI.rmquote(tmp); nextSibling.innerHTML=' '+tmp;UI.render_canvas(nextSibling);">ok</button><span></span><br>} \else \lstinline@#2@ \fi }
If hevea
compiles the command, the \ifhevea
part is
active, and the command will output an HTML5 <textarea>
element
and a OK <button>
, with a callback to JavaScript code
that will evaluate the CAS command inside the textarea
var tmp=UI.caseval(previousSibling.value)
and fill the next HTML5 <span>
field with the result of the CAS
command.
The CAS evaluation is performed by a call to giaceval
in the
UI.caseval
code (defined in giac.tex
), where
giaceval
is a global JavaScript variable assigned at page loadtime
from the Module
interface created by compiling Giac/Xcas with
the C++ to JavaScript compiler
emscripten.
The CAS code being in JavaScript, it can be run on every
JavaScriptenabled browser. It will be faster on browsers that have
support for asm.js
(asmjs.org
)
like Mozilla Firefox: numerical computations
are 1 to 2 times slower than native code, while exact computations
are 2 to 10 times slower than native code (the main reason being that
JavaScript has currently no 64 bits integer type).
For a PDF output, if pdflatex
is run on the tex file,
giac commands will be written verbatim, but they will not be processed.
The icas
command from the Giac/Xcas package will filter all
giac commands, process them and output the result in math mode in a
temporary L^{A}T_{E}X file. If the
answer is a 2d graph output, icas
will output a pdf file on
the hard disk and output a corresponding \includegraphics
command in the temporary L^{A}T_{E}X file. After that, the temporary file
will be processed by pdflatex
.
4 Conclusion
The current version of icas
and giac.tex
are already
usable to easily produce HTML interactive CASenabled document from
L^{A}T_{E}X documents. They may be completed in future versions depending
on user requests. For example, online courses might have commands to
enable student exercises answers autocheck.
Acknowledgements
Thanks to Luc Maranget and Yannick Chevalier for fixing bugs in
mathjaxenabled hevea.
Thanks to Renée De Graeve and Murielle Stepec who have tested
preliminary versions of this compilation method.
References
 [1]
 Yannick Chevallier. Hevea: LaTeX to HTML5 compiler, fork for MathJax support. https://github.com/YannickChevalier/heveamathjax, 2017.
 [2]
 Dan Drake. SageTex. https://www.ctan.org/pkg/sagetex, 2009.
 [3]
 Jacques Distler. LaTeX to MathML converter. golem.ph.utexas.edu/ distler/blog/itex2MML.html, 2016.
 [4]
 JeanMichel Sarlat. pgiac. http://melusine.eu.org/syracuse/giac/pgiac/, 2011.
 [5]
 Joris van der Hoeven. Texmacs. http://www.texmacs.org/, 2017.
 [6]
 Luc Maranget. Hevea: LaTeX to HTML5 compiler (unstable version). http://hevea.inria.fr/distri/unstable/, 2017.
 [7]
 Matthias Ettrich. Lyx. https://ww.lyx.org, 2012.
 [8]
 NumFOCUS Foundation. The Jupyter Notebook. jupyter.org, 2017.
 [9]
 Bernard Parisse. LaTeX to Mathml converter, fork for hevea output support. wwwfourier.ujfgrenoble.fr/ parisse/giac/heveatomml.tgz, 2017.
 [10]
 Bernard Parisse and Renée De Graeve. Giac/Xcas Computer Algebra System. wwwfourier.ujfgrenoble.fr/ parisse/giac.html, 2017.
 [11]
 Alon Zakai. Emscripten: A C/C++ to Javascript compiler. kripken.github.io/emscriptensite/, 2017.