Difference: LaTeX (7 vs. 8)

Space squeezing

Spacing displays

• Spacing in displays. Usually it's best to leave the spacing up to TeX. However, if explicit horizontal spacing is needed (for example, to set an expression like (n \to \infty) apart from the rest of the display, or to separate two equations on the same line), \quad in most cases generates the right amount of space. Don't try to create spacing with a bunch of explicit spaces ("\ "); the spacing generated in this way is usually not optimal, and the explicit spaces will likely have to be removed (and possibly replaced by \quad) when the paper is typeset at the publisher's end.
• Avoid blank lines before or after a display, unless you really want to start a new paragraph: It is tempting to surround displayed math material by blank lines in the source file, to make them stand out and easier to locate. However, this is usually wrong, since blank lines are interpreted as paragraph breaks, may generate some additional vertical spacing and cause the next line of text to be indented - something you usually don't want. If you want to set off displays in your source file, do so by inserting a line with comment symbols, such as %%%%% equation 3.1 %%%%%%%%%%%%%% before and/or after the display.
• Correcting underful vboxes and bad page breaks. By default, TeX does not break pages inside display environments such as align. If a paper has many multiline formulas, this may cause "underful vboxes", which can look very poor if the badness (reported by tex in the log file) is a few thousand. One way to remedy this is to put the command \allowdisplaybreaks in the preamble. However, this may cause some poor pagebreaks which may have to be fixed. A compromise solution is to use \allowdisplaybreaks locally, on the individual displays that cause problems: {\allowdisplaybreaks \begin{align} ... \end{align} }. The best solution is to prevent this problem by avoiding excessively long displays (say, with five or more lines). It is often not hard to break up a very long display into two, for example by inserting a phrase like "By the Cauchy-Schwarz inequality, the last expression is at most" in the middle of the overlong display, followed by the remaining lines of the display.
• Multiline subscripts on sums or integrals. Use the \substack{...} command, which works much like the \sb ... \endsb pair in amstex. It is much easier to use, and produces better looking output than an array environment or a construct using \atop (derived from plain tex).

Useful links