# Question:Latex generates wrong Latex for this example

## Question:Latex generates wrong Latex for this example

Maple 2020

Please see this example. This Latex generated gives Latex compile error.

restart;
Latex:-Settings(UseImaginaryUnit=i,
UseColor = false,
powersoftrigonometricfunctions= mixed, ## computernotation,
leavespaceafterfunctionname = true,
cacheresults = false,
spaceaftersqrt = true
);

L:=3;
c:=4;
h:=1/10;
b:=Pi*c/L;
f:=piecewise(0<x and x<L/3,3*h/L*x,L/3<x and x<L,h);
pde := diff(u(x,t),t$2) + b*diff(u(x,t),t) = c^2*diff(u(x,t),x$2);
bc  := u(0,t)=0,D[1](u)(L,t)=0;
ic  := D[2](u)(x,0)=0,u(x,0)=f;
sol:=pdsolve([pde,bc,ic],u(x,t));


The Latex generated does not compile:

Latex(sol)

u \left(x , t\right) =
\Mapleoverset{\infty}{\Mapleunderset{n =0}{\sum}}\left\{\begin{array}{44}\frac{4 \,{\mathrm e}^{-\frac{2 t \pi}{3}} \left(t \pi +\frac{3}{2}\right) \sin \left(\frac{\pi  x}{6}\right)}{5 \pi^{2}} & n =0 \\\frac{3 \sin \left(\frac{\left(1+2 n \right) \pi  x}{6}\right) \left(\sqrt{3}\, \sin \left(\frac{\pi  n}{3}\right)+\cos \left(\frac{\pi  n}{3}\right)\right) \left(\left(2 \sqrt{n}\, \sqrt{n +1}+i\right) {\mathrm e}^{\frac{2 i \pi  \left(-2 \sqrt{n}\, \sqrt{n +1}+i\right) t}{3}}-{\mathrm e}^{\frac{2 i \pi  \left(2 \sqrt{n}\, \sqrt{n +1}+i\right) t}{3}} \left(-2 \sqrt{n}\, \sqrt{n +1}+i\right)\right)}{10 \sqrt{n}\, \sqrt{n +1}\, \pi^{2} \left(1+2 n \right)^{2}} & \mathit{otherwise}  \end{array}\right.


Gives

\documentclass[11pt]{article}
\usepackage{amsmath}
\usepackage{maplestd2e}

\begin{document}
$u \left(x , t\right) = \Mapleoverset{\infty}{\Mapleunderset{n =0}{\sum}}\left\{\begin{array}{44}\frac{4 \,{\mathrm e}^{-\frac{2 t \pi}{3}} \left(t \pi +\frac{3}{2}\right) \sin \left(\frac{\pi x}{6}\right)}{5 \pi^{2}} & n =0 \\\frac{3 \sin \left(\frac{\left(1+2 n \right) \pi x}{6}\right) \left(\sqrt{3}\, \sin \left(\frac{\pi n}{3}\right)+\cos \left(\frac{\pi n}{3}\right)\right) \left(\left(2 \sqrt{n}\, \sqrt{n +1}+i\right) {\mathrm e}^{\frac{2 i \pi \left(-2 \sqrt{n}\, \sqrt{n +1}+i\right) t}{3}}-{\mathrm e}^{\frac{2 i \pi \left(2 \sqrt{n}\, \sqrt{n +1}+i\right) t}{3}} \left(-2 \sqrt{n}\, \sqrt{n +1}+i\right)\right)}{10 \sqrt{n}\, \sqrt{n +1}\, \pi^{2} \left(1+2 n \right)^{2}} & \mathit{otherwise} \end{array}\right.$

\end{document}


This, using latest TeXLive on Linux, gives  Illegal character in array arg.

lualatex foo5.tex
This is LuaHBTeX, Version 1.12.0 (TeX Live 2020)
restricted system commands enabled.
(./foo5.tex
LaTeX2e <2020-10-01> patch level 2

L3 programming layer <2020-12-07> xparse <2020-03-03> (/usr/local/texlive/2020/texmf-dist/tex/latex/base/article.cls
Document Class: article 2020/04/10 v1.4m Standard LaTeX document class
(/usr/local/texlive/2020/texmf-dist/tex/latex/base/size11.clo)) (/usr/local/texlive/2020/texmf-dist/tex/latex/amsmath/amsmath.sty
For additional information on amsmath, use the ?' option.
(/usr/local/texlive/2020/texmf-dist/tex/latex/amsmath/amstext.sty (/usr/local/texlive/2020/texmf-dist/tex/latex/amsmath/amsgen.sty)) (/usr/local/texlive/2020/texmf-dist/tex/latex/amsmath/amsbsy.sty) (/usr/local/texlive/2020/texmf-dist/tex/latex/amsmath/amsopn.sty)) (/mnt/g/public_html/styles/maplestd2e.sty
Package: maple2e 2005/03/17 v1.16
Defining Maple Utility Macros
(/mnt/g/public_html/styles/mapleenv.def)
Defining Maple Plot Environemnts
...Defaults to "dvips" Driver
(/usr/local/texlive/2020/texmf-dist/tex/latex/graphics/epsfig.sty (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics/graphicx.sty (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics/keyval.sty) (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics/graphics.sty (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics/trig.sty) (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics-cfg/graphics.cfg) (/usr/local/texlive/2020/texmf-dist/tex/latex/graphics-def/dvips.def))))
Defining Automatic Style Generation Macros
) (/usr/local/texlive/2020/texmf-dist/tex/latex/l3backend/l3backend-luatex.def) (./foo5.aux) (/usr/local/texlive/2020/texmf-dist/tex/latex/base/ts1cmr.fd)

! LaTeX Error: Illegal character in array arg.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
...haracter\or Missing @-exp\or Missing p-arg\fi \space in array arg.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help\@err@

l.8 \Mapleoverset{\infty}{\Mapleunderset{n =0}{\sum}}\left\{\begin{array}{44}
\frac{4 \,{\mathrm e}^{-\frac{2 t \pi}{3}}
?


fyi. No errors are generated from the old latex() command.

The following is another example, with the same Latex error.

restart;
Latex:-Settings(UseImaginaryUnit=i,
UseColor = false,
powersoftrigonometricfunctions= mixed, ## computernotation,
leavespaceafterfunctionname = true,
cacheresults = false,
spaceaftersqrt = true
);

c:=3;
f:=piecewise(4<x and x<5,1,true,0);
pde := diff(u(x, t), t$2) = c^2*(diff(u(x, t), x$2));
bc  := eval( diff(u(x,t),x),x=0)=0;
ic  := u(x,0)=f(x),eval(diff(u(x,t),t),t=0)=0;
sol:=pdsolve([pde, bc,ic],u(x,t)) assuming x>0,t>0;

Latex(sol);  #gives Latex that do not compile`

Maple 2020.2, with Physics 897

﻿