Eliminating Underfull Boxes: Causes And Solutions In Latex

Understanding Underfull Boxes

An underfull box in LaTeX refers to a line of text that does not properly fill the entire width allocated to it by the document's margins. This can result in too much whitespace on some lines, leading to inconsistent spacing and odd gaps that disrupt the visual flow of text.

Underfull boxes occur due to the complex way LaTeX handles line breaks and text justification. By default, LaTeX aims to produce fully-justified text with straight margins on both left and right sides. To achieve this, it carefully calculates line breaks to make each line as close to the text width as possible, while also avoiding hyphenation where not desired.

Despite LaTeX's sophisticated typesetting algorithms, certain text combinations can confuse its line break calculations. If a line ends up much shorter than the allocated text width, this leads to an underfull box warning in the LaTeX log. The resulting line in the PDF may have a ragged appearance, too much whitespace, and inconsistent spacing compared to surrounding text.

Identifying Underfull Boxes

When LaTeX encounters underfull boxes during typesetting, it generates warnings in the log file, showing a percentage representing how much the line falls short of the expected width. For example:

Underfull \hbox (badness 10000) detected at line 576 []|\OT1/cmr/m/n/10 This is some short text

A "badness" value over 4000 typically indicates a visible spacing problem needing correction. In the compiled PDF, underfull lines stand out due to extra whitespace. But confirming and locating them without the log can be tricky.

The LaTeX \usepackage{showframe} reveals text boundaries, highlighting issues like underfull lines. The \disablehyphenation command also helps intensify the effect by disrupting LaTeX justification and collisions where words could hyphenate or wrap.

Fixing Underfull Boxes

Solving underfull boxes involves investigating why LaTeX failed to find an optimal break point for that troublesome line. Adjusting text formatting, whitespace, hyphenation and document margins can help guide LaTeX towards better typesetting choices.

Adjusting Whitespace and Line Breaks

Because underfull lines mean a line runs short without enough content, removing all explicit line breaks is a good first step. Next, delete any unnecessary spaces before considering the addition of custom breaks with \linebreak to coerce the paragraph into better forming longer lines.

Hard-coded line and page formatting commands like \linebreak also give manual control. Although labor intensive for long documents, strategic use in problematic paragraphs provides LaTeX more layout freedom and cuts reliance on automated line breaking.

Modifying Paragraph and Text Formatting

Changing text justification and indentation can also improve underfull lines by altering LaTeX’s typesetting targets. For example, ragged right text alignment removes the requirement to stretch lines to both margins.

Formatting like font sizes, line heights, margins and columns introduces constraints for LaTeX to work within. Experimenting with these values may change pagination and create better break point options to utilize available horizontal space.

Using relative unit sizes like ems for key paragraphs rather than fixed values also helps LaTeX dynamically fit content during typesetting, avoiding widths that compete with mandatory spaces.

Using microtype and Other Packages

More advanced typesetting systems like microtype subtly adjust spacing and protrusion to rectify lines. Enabling its automatic expansion and shrinking helps regulate tiny width fluctuations.

Packages like ragtag improve document appearance by justifying edges more aggressively with wider word spacing. Similarly, linegoal relies on manual spacing targets instead of automated break point calculations.

Flexibility from these packages relieves LaTeX of difficult typesetting judgements. But too much visual disruption risks readability. The ideal values require experimentation to suit both appearance and meaning.

Allowing Hyphenation

Text needing to wrap across lines risks underfull results when words exceed the maximum length. This hinders ideal break points mid-paragraph.

Enabling LaTeX hyphenation with \hyphenation and dictionaries gives more options hyphenate long words. This can create tighter lines through word splitting, instead of short lines with wide spaces from pushing entire overflow words to the next line.

However manual intervention helps avoid poor hyphenation choices. Specifying custom break points with \- provides cleaner results for very long words prone to awkward divisions.

Changing Document Margins

Sometimes underfull lines persist without enough horizontal space for options. In these cases, widening margins increases text width. This provides LaTeX more opportunities to achieve the right amount of text for the expected appearance.

However, margin adjustment risks disrupting page layouts and vertical spacing between elements like figures and tables. More content per line could also introduce more hyphenation, boxes with overspilling text, or oddly stretched justification.

Example Code for Eliminating Underfull Boxes

Here are some LaTeX code snippets for eliminating common underfull box cases, along with before and after examples demonstrating improvements:

Short Text Snippets


This is some short text in \LaTeX that generates an underfull box with lots of trailing whitespace.


This is some short text with manual breaks (\linebreak, \newline) in \LaTeX that generates (\linebreak) an underfull box with lots of (\linebreak) trailing whitespace.  

Long URLs and Links


An example link shows bad wrapping across lines for long URLs like this: 


An example link shows better wrapping for long URLs like this: \linebreak  
https://www.verylongurl.com/with/many/levels/\linebreak that/has/underfull/lines

Disabling Whitespace Around Graphics

\includegraphics{diagram} cause spacing issues if LaTeX puts extra whitespace above or below them:

This text has an awkward gap from the image whitespace.


\noindent \includegraphics[trim=0 0 50 50, clip, width=\linewidth]{diagram} remove extra spacing around images so text flows tighter:  

This text has improved spacing from trimmed graphics.

Achieving Optimal Typesetting

Good page design involves balancing between underfull and overfull boxes. Too many adjustments to fix lines that run short risks options running long, overflowing into margins.

Experimentation provides typographic nuance - an acceptable amount of variation keeps text interesting. The odd line ending 10-20\% short sometimes passes unnoticed, and over-correction risks new problems.

However allowing any lines exceeding the text block looks unprofessional. Careful inspection at high zoom levels catches small alignment and positioning flaws before finalizing projects.

Validation tools like LaTeX Analyse Package Statistics also give an overview of document typesetting. Keeping warnings below 5\% avoids glaring flaws, while monitoring improvement during editing.

With practice, LaTeX conventions make underfull lines rarer. But as a complex automated typesetting language, some remaining aesthetic judgement calls persist. There is no single formula guarantees perfection - but learning why lines break poorly gives control over long documents.

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