[Tex/LaTex] How to fix Underfull \vbox

debugging

I am trying to compile some chapters with the main file thesis.tex in TeXmaker.

After compiling it returns:

 Chapter 4.
 (./chapter/res.tex)
 Underfull \vbox (badness 10000) has occurred while \output is active []
[11
]

I'm new to latex, how can I understand and solve that warning?

Best Answer

You have given very few clues but I assume you have done this

\documentclass[twoside]{report}

\setlength\parskip{1em}

\begin{document}


one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 


\end{document}

which produces the warning

Underfull \vbox (badness 10000) has occurred while \output is active [1

The problem is that the document class has specified that the last line of each page should be at the bottom of the page, but you have removed all flexibility from \parskip and set it to a length which is not a multiple of \baselineskip.

The standard classes default the textheight to be \topskip plus a multiple of \baselineskip precisely to avoid this problem, so a page full of text fits the page exactly. But if you have a page with no stretchable space (so no headings or lists or equations that have stretch space around them) and you have set \parskip to a value that does not stretch, and is not a multiple of \baselineskip then the page inevitably ends short and there is no way to expand it to fill the specified space so it is underfull.

If instead of 1em you set

\setlength\parskip{\baselineskip}

or 

\setlength\parskip{1em plus 2pt}

then the warning goes and the bottom line of text is at the bottom of the page.

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