amsmath

amsmath is a LaTeX package produced by the American Mathematical Society to improve the presentation of mathematical content. It extends the standard math features of LaTeX by adding flexible environments for multiline formulas, new alignment tools, and better handling of equation numbering. The package is widely used as part of the AMS-LaTeX distribution and is typically loaded with \usepackage{amsmath} in the document preamble, often together with amssymb and amsfonts.

Key features include a collection of environments for multi-line and aligned equations: align and align* for aligned equations with automatic numbering, gather and gather* for groups of equations, alignat and flalign for fine-grained alignment, multline for long equations that span multiple lines, and split for splitting a single equation within the equation environment. A number of supporting environments such as cases for piecewise definitions, and aligned and alignedat for embedding formulas into other math structures are provided. It also improves the handling of text inside math mode via \text, allows manual equation tagging with \tag, and supports resetting numbering with \numberwithin. The package enhances delimiter sizing, spacing, and overall readability of complex formulas.

amsmath is designed to be compatible with other AMS tools, and is commonly used in conjunction with amssymb and amsfonts. Users can customize referencing using showonlyrefs and other options, and are encouraged to refer to the package documentation for full details.