Sstrhsrtj

I know that formula expression is mistyped, but I dont know why pdfTex is frozen(possibly infinite loop) instead of quting nicely? Is there a workaround? Because in case of an erronous input, I need to restart my server.

documentclass{article}

usepackage{graphicx}

usepackage{draftwatermark}

usepackage{breqn}

usepackage{amsmath}

SetWatermarkText{FAST MATH}

SetWatermarkScale{2}

SetWatermarkVerCenter{0.6paperheight}

SetWatermarkAngle{30}



begin{document}



section{Input}

$left. begin{array} { l } { a ) A = { 2   $

section{Solution}

${a: 0}$

end{document}

The issue can be reproduced with a smaller example, showing it has nothing to do with the loaded packages:

documentclass{article}



begin{document}



$left. begin{array} { l } { a ) A = { 2   $



section{Solution}

${a: 0}$



end{document}

The errors in the math formula, followed by the section title, make TeX enter an infinite loop announced by

! LaTeX Error: begin{array} on input line 7 ended by end{document}.



See the LaTeX manual or LaTeX Companion for explanation.

Type  H <return>  for immediate help.

 ...                                              



l.12 end{document}



? 



! Improper prevdepth.

newpage ...everypar {}fi par ifdim prevdepth 

                                                  >z@ vskip -ifdim prevd...

l.12 end{document}

The missing end{array} causes par to still be defined as “do nothing” like it always is in array. Since the error recovery here is to try doing end{document}, LaTeX tries to finish up the page issuing par, which does nothing.

If we add tracingmacros=1, after the last error message we see, in the log file after interrupting the program, a string of

par ->



par ->



par ->



par ->



par ->

Solution: don't make silly errors in your input.

Another solution could be running pdflatex with the option -halt-on-error, which would stop it at the first error.

However, this is not foolproof. If the user has deffoo{foo} in their preamble, then the first usage of foo in the document would start an infinite loop with no error.

You have unbalanced environments/braces; begin{array} doesn't have end{array} and left. doesn't have right... Also, load breqn after amsmath and add lmodern for preventing missing font sizes substitution.

documentclass{article}

usepackage{graphicx,lmodern}

usepackage{draftwatermark}

usepackage{amsmath}

usepackage{breqn}

SetWatermarkText{FAST MATH}

SetWatermarkScale{2}

SetWatermarkVerCenter{0.6paperheight}

SetWatermarkAngle{30}



begin{document}



section{Input}

$ begin{array} { l }  a) A = { 2  end{array}$

section{Solution}

${a: 0}$



end{document}

I am not sure of what you are trying to typeset, but please try the following

documentclass{article}

usepackage{graphicx}

usepackage{draftwatermark}

usepackage{amsmath}



SetWatermarkText{FAST MATH}

SetWatermarkScale{0.8}

SetWatermarkVerCenter{0.6paperheight}

SetWatermarkAngle{30}



begin{document}



section{Input}

begin{equation}

left. begin{array}{c}

l \

a \

end{array} right), quad A = { 2

end{equation}

section{Solution}

${a: 0}$

end{document}

Please use compiler XeLaTeX.

It seems that I am unable to comment on a comment. Weird system or what?

So I am making this into an unsatisfactory answer to your question about the existence of a “workaround” your particular class of “unavoidable silly (or unavoidably silly?) errors”

@heral: (Trying to be nice!) Yes, we are all, well most of us, often silly and we make many errors.
But that is not sufficient reason for there being “workarounds” for all of the silly errrors made by you, and also those made by everyone else.

More technically: It is regrettable that some errors, even some that are non-silly and avoidable, lead to non-space filling recursion (causing an infinite loop or ‘hanging’). There is a theorem somewhere stating that any sufficiently useful software system will provide the possibility of such ‘hanging’ errors and, moreover, that it is impossible to know about and hence trap them all. — no Universal Workarounds! Tough!)