LaTeX
Encyclopedia
LaTeX is a document markup language and document preparation system
for the TeX
typesetting
program. Within the typesetting system, its name is styled as . The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. In order to create a document in LaTeX, a .tex file must be created using some form of text editor
. While most text editors can be used to create a LaTeX document, a number of editors have been created specifically for working with LaTeX.
LaTeX is widely used in academia
. As a primary or intermediate format, e.g., translating DocBook
and other XML
-based formats to PDF, LaTeX is used because of the high quality of typesetting
achievable by TeX. The typesetting system offers programmable desktop publishing
features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout and bibliographies
.
LaTeX is intended to provide a high-level language that accesses the power of TeX. LaTeX essentially comprises a collection of TeX macros and a program to process LaTeX documents. Because the TeX formatting commands are very low-level, it is usually much simpler for end-users to use LaTeX.
LaTeX was originally written in the early 1980s by Leslie Lamport
at SRI International
. It has become an important method for using TeX. The current version is LaTeX2e (styled as ).
As it is distributed under the terms of the LaTeX Project Public License (LPPL), LaTeX is free software
.
s allow styles to be defined globally for an entire document or the use of Cascading Style Sheets
to style HTML
.
LaTeX can be arbitrarily extended by using the underlying macro language to develop custom formats. Such macros are often collected into packages, which are available to address special formatting issues such as complicated mathematical content or graphics. Indeed, in the example below, the
, but with a /k/).
The characters T, E, X in the name come from capital Greek
letters tau
, epsilon
, and chi
, as the name of TeX
derives from the (skill, art, technique); for this reason, TeX's creator Donald Knuth
promotes a pronunciation of ˈ (that is, with a voiceless velar fricative
as in Modern Greek, similar to the last sound of the German word "Bach", the Spanish "j" sound, or as ch in loch
). Lamport, on the other hand, has said he does not favor or discourage any pronunciation for LaTeX.
The name is traditionally printed with the special typographical logo
shown at the top of this page.
In media where the logo cannot be precisely reproduced in running text, the word is typically given the unique capitalization LaTeX. The TeX, LaTeX and XeTeX
logos can be rendered via pure CSS
and XHTML
for use in graphical web browser
s following the specifications of the internal \LaTeX macro.
. It is distributed under a free software license, the LaTeX Project Public License
(LPPL). The LPPL is not compatible with the GNU General Public License
, as it requires that modified files must be clearly differentiable from their originals (usually by changing the filename); this was done to ensure that files that depend on other files will produce the expected behavior and avoid dependency hell
. The LPPL is DFSG
compliant as of version 1.3. As free software
, LaTeX is available on most operating systems including UNIX
(Mac OS X
, Solaris), UNIX
system-like OS (Linux OS
, BSDs, OpenSolaris
), Microsoft Windows
, RISC OS
and AmigaOS
.
.
When TeX "compiles" a document, the processing sequence (from the user's point of view) goes like this: Macros > TeX > Driver > Output. Different implementations of each of these steps are typically available in TeX distributions. Traditional TeX will output a DVI
file, which is usually converted to a PostScript
file. More recently, Hàn Thế Thành and others have written a new implementation of TeX called pdfTeX
, which also outputs to PDF and takes advantage of features available in that format. The XeTeX
engine developed by Jonathan Kew merges modern font technologies and Unicode with TeX.
The default font for LaTeX is Knuth's Computer Modern
, which gives default documents created with LaTeX the same distinctive look as those created with plain TeX. XeTeX allows the use of OpenType and TrueType (that is, outlined) fonts for output files.
There are also many editors for LaTeX
.
support, a new user interface, access to arbitrary fonts, and new documentation.
There are numerous commercial implementations of the entire TeX system. System vendors may add extra features like additional typeface
s and telephone support. LyX
is a free
, WYSIWYM
visual document processor that uses LaTeX for a back-end. TeXmacs is a free
, WYSIWYG
editor with similar functionalities as LaTeX but a different typesetting engine. Other WYSIWYG editors that produce LaTeX include Scientific Word on MS Windows.
A number of TeX distributions are available, including TeX Live
(multiplatform), teTeX
(deprecated in favour of TeX Live, UNIX), fpTeX (deprecated), MiKTeX
(Windows), proTeXt
(Windows), MacTeX
(TeX Live with the addition of Mac specific programs), gwTeX (Mac OS X), OzTeX (Mac OS Classic), AmigaTeX (no longer available) Latexian (Mac OS X) and PasTeX (AmigaOS, available on the Aminet
repository).
or OpenOffice.org Writer
by converting the LaTeX file (.tex) to Rich Text Format
(.rtf) or XML
. This can be done using the free software programs LaTeX2RTF
or TeX4ht
.
Word processor
A word processor is a computer application used for the production of any sort of printable material....
for the TeX
TeX
TeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....
typesetting
Typesetting
Typesetting is the composition of text by means of types.Typesetting requires the prior process of designing a font and storing it in some manner...
program. Within the typesetting system, its name is styled as . The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. In order to create a document in LaTeX, a .tex file must be created using some form of text editor
Text editor
A text editor is a type of program used for editing plain text files.Text editors are often provided with operating systems or software development packages, and can be used to change configuration files and programming language source code....
. While most text editors can be used to create a LaTeX document, a number of editors have been created specifically for working with LaTeX.
LaTeX is widely used in academia
Academia
Academia is the community of students and scholars engaged in higher education and research.-Etymology:The word comes from the akademeia in ancient Greece. Outside the city walls of Athens, the gymnasium was made famous by Plato as a center of learning...
. As a primary or intermediate format, e.g., translating DocBook
DocBook
DocBook is a semantic markup language for technical documentation. It was originally intended for writing technical documents related to computer hardware and software but it can be used for any other sort of documentation....
and other XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
-based formats to PDF, LaTeX is used because of the high quality of typesetting
Typesetting
Typesetting is the composition of text by means of types.Typesetting requires the prior process of designing a font and storing it in some manner...
achievable by TeX. The typesetting system offers programmable desktop publishing
Desktop publishing
Desktop publishing is the creation of documents using page layout software on a personal computer.The term has been used for publishing at all levels, from small-circulation documents such as local newsletters to books, magazines and newspapers...
features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout and bibliographies
Bibliography
Bibliography , as a practice, is the academic study of books as physical, cultural objects; in this sense, it is also known as bibliology...
.
LaTeX is intended to provide a high-level language that accesses the power of TeX. LaTeX essentially comprises a collection of TeX macros and a program to process LaTeX documents. Because the TeX formatting commands are very low-level, it is usually much simpler for end-users to use LaTeX.
LaTeX was originally written in the early 1980s by Leslie Lamport
Leslie Lamport
Leslie Lamport is an American computer scientist. A graduate of the Bronx High School of Science, he received a B.S. in mathematics from the Massachusetts Institute of Technology in 1960, and M.A. and Ph.D. degrees in mathematics from Brandeis University, respectively in 1963 and 1972...
at SRI International
SRI International
SRI International , founded as Stanford Research Institute, is one of the world's largest contract research institutes. Based in Menlo Park, California, the trustees of Stanford University established it in 1946 as a center of innovation to support economic development in the region. It was later...
. It has become an important method for using TeX. The current version is LaTeX2e (styled as ).
As it is distributed under the terms of the LaTeX Project Public License (LPPL), LaTeX is free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
.
Typesetting system
LaTeX is based on the idea that authors should be able to focus on the content of what they are writing without being distracted by its visual presentation. In preparing a LaTeX document, the author specifies the logical structure using familiar concepts such as chapter, section, table, figure, etc., and lets the LaTeX system worry about the presentation of these structures. It therefore encourages the separation of layout from content while still allowing manual typesetting adjustments where needed. This is similar to the mechanism by which many word processorWord processor
A word processor is a computer application used for the production of any sort of printable material....
s allow styles to be defined globally for an entire document or the use of Cascading Style Sheets
Cascading Style Sheets
Cascading Style Sheets is a style sheet language used to describe the presentation semantics of a document written in a markup language...
to style HTML
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
.
LaTeX can be arbitrarily extended by using the underlying macro language to develop custom formats. Such macros are often collected into packages, which are available to address special formatting issues such as complicated mathematical content or graphics. Indeed, in the example below, the
align environment is provided by the amsmath package.Examples
The example below shows the LaTeX input and corresponding output:\documentclass[12pt]{article} \usepackage{amsmath} \title{\LaTeX} \date{} \begin{document} \maketitle \LaTeX{} is a document preparation system for the \TeX{} typesetting program. It offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout, bibliographies, and much more. \LaTeX{} was originally written in 1984 by Leslie Lamport and has become the dominant method for using \TeX; few people write in plain \TeX{} anymore. The current version is \LaTeXe. % This is a comment; it will not be shown in the final output. % The following shows a little of the typesetting power of LaTeX: \begin{align} E &= mc^2 \\ m &= \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}} \end{align} \end{document} |
Pronouncing and writing "LaTeX"
LaTeX is usually pronounced ˈ or ˈ in English (that is, not with the /ks/ pronunciation English speakers normally associate with XX
X is the twenty-fourth letter in the basic modern Latin alphabet.-Uses:In mathematics, x is commonly used as the name for an independent variable or unknown value. The usage of x to represent an independent or unknown variable can be traced back to the Arabic word šay شيء = “thing,” used in Arabic...
, but with a /k/).
The characters T, E, X in the name come from capital Greek
Greek alphabet
The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
letters tau
Tau
Tau is the 19th letter of the Greek alphabet. In the system of Greek numerals it has a value of 300.The name in English is pronounced , but in modern Greek it is...
, epsilon
Epsilon
Epsilon is the fifth letter of the Greek alphabet, corresponding phonetically to a close-mid front unrounded vowel . In the system of Greek numerals it has a value of 5. It was derived from the Phoenician letter He...
, and chi
Chi (letter)
Chi is the 22nd letter of the Greek alphabet, pronounced as in English.-Greek:-Ancient Greek:Its value in Ancient Greek was an aspirated velar stop .-Koine Greek:...
, as the name of TeX
TeX
TeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....
derives from the (skill, art, technique); for this reason, TeX's creator Donald Knuth
Donald Knuth
Donald Ervin Knuth is a computer scientist and Professor Emeritus at Stanford University.He is the author of the seminal multi-volume work The Art of Computer Programming. Knuth has been called the "father" of the analysis of algorithms...
promotes a pronunciation of ˈ (that is, with a voiceless velar fricative
Voiceless velar fricative
The voiceless velar fricative is a type of consonantal sound used in some spoken languages. The sound was part of the consonant inventory of Old English and can still be found in some dialects of English, most notably in Scottish English....
as in Modern Greek, similar to the last sound of the German word "Bach", the Spanish "j" sound, or as ch in loch
Loch
Loch is the Irish and Scottish Gaelic word for a lake or a sea inlet. It has been anglicised as lough, although this is pronounced the same way as loch. Some lochs could also be called a firth, fjord, estuary, strait or bay...
). Lamport, on the other hand, has said he does not favor or discourage any pronunciation for LaTeX.
The name is traditionally printed with the special typographical logo
Logo
A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition...
shown at the top of this page.
In media where the logo cannot be precisely reproduced in running text, the word is typically given the unique capitalization LaTeX. The TeX, LaTeX and XeTeX
XeTeX
XeTeX is a TeX typesetting engine using Unicode and supporting modern font technologies such as OpenType or Apple Advanced Typography...
logos can be rendered via pure CSS
CSS
-Computing:*Cascading Style Sheets, a language used to describe the style of document presentations in web development*Central Structure Store in the PHIGS 3D API*Closed source software, software that is not distributed with source code...
and XHTML
XHTML
XHTML is a family of XML markup languages that mirror or extend versions of the widely-used Hypertext Markup Language , the language in which web pages are written....
for use in graphical web browser
Web browser
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
s following the specifications of the internal \LaTeX macro.
Licensing
LaTeX is typically distributed along with plain TeXTeX
TeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....
. It is distributed under a free software license, the LaTeX Project Public License
LaTeX Project Public License
The LaTeX Project Public License is a software license originally written for the LaTeX system. Software distributed under the terms of the LPPL can be regarded as free software, however it is not copylefted....
(LPPL). The LPPL is not compatible with the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
, as it requires that modified files must be clearly differentiable from their originals (usually by changing the filename); this was done to ensure that files that depend on other files will produce the expected behavior and avoid dependency hell
Dependency hell
Dependency hell is a colloquial term for the frustration of some software users who have installed software packages which have dependencies on specific versions of other software packages. This was mainly attributable to old Linux package managers...
. The LPPL is DFSG
Debian Free Software Guidelines
The Debian Free Software Guidelines is a set of guidelines that the Debian Project uses to determine whether a software license is a free software license, which in turn is used to determine whether a piece of software can be included in Debian...
compliant as of version 1.3. As free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
, LaTeX is available on most operating systems including UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
(Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, Solaris), UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
system-like OS (Linux OS
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, BSDs, OpenSolaris
OpenSolaris
OpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
), Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, RISC OS
RISC OS
RISC OS is a computer operating system originally developed by Acorn Computers Ltd in Cambridge, England for their range of desktop computers, based on their own ARM architecture. First released in 1987, under the name Arthur, the subsequent iteration was renamed as in 1988...
and AmigaOS
AmigaOS
AmigaOS is the default native operating system of the Amiga personal computer. It was developed first by Commodore International, and initially introduced in 1985 with the Amiga 1000...
.
Related software
As a macro package, LaTeX provides a set of macros for TeX to interpret. There are many other macro packages for TeX, including Plain TeX, GNU Texinfo, AMSTeX, and ConTeXtConTeXt
ConTeXt is a general-purpose document processor. It is especially suited for structured documents, automated document production, very fine typography, and multi-lingual typesetting. It is based in part on the TeX typesetting system, and uses a document markup language for manuscript preparation...
.
When TeX "compiles" a document, the processing sequence (from the user's point of view) goes like this: Macros > TeX > Driver > Output. Different implementations of each of these steps are typically available in TeX distributions. Traditional TeX will output a DVI
DVI (file format)
The Device independent file format is the output file format of the TeX typesetting program, designed by David R. Fuchs in 1979. Unlike the TeX markup files used to generate them, DVI files are not intended to be human-readable; they consist of binary data describing the visual layout of a...
file, which is usually converted to a PostScript
PostScript
PostScript is a dynamically typed concatenative programming language created by John Warnock and Charles Geschke in 1982. It is best known for its use as a page description language in the electronic and desktop publishing areas. Adobe PostScript 3 is also the worldwide printing and imaging...
file. More recently, Hàn Thế Thành and others have written a new implementation of TeX called pdfTeX
PdfTeX
The computer program pdfTeX is an extension of Knuth's typesetting program TeX, and was originally written and developed into a publicly usable product by Hàn Thế Thành as a part of the work for his PhD thesis at the Faculty of Informatics, Masaryk University, Brno...
, which also outputs to PDF and takes advantage of features available in that format. The XeTeX
XeTeX
XeTeX is a TeX typesetting engine using Unicode and supporting modern font technologies such as OpenType or Apple Advanced Typography...
engine developed by Jonathan Kew merges modern font technologies and Unicode with TeX.
The default font for LaTeX is Knuth's Computer Modern
Computer Modern
Computer Modern is the family of typefaces used by default by the typesetting program TeX. It was created by Donald Knuth with his METAFONT program, and was most recently updated in 1992. However, the family font was superseded by CM-Super , the latest release dating 2008...
, which gives default documents created with LaTeX the same distinctive look as those created with plain TeX. XeTeX allows the use of OpenType and TrueType (that is, outlined) fonts for output files.
There are also many editors for LaTeX
Comparison of TeX editors
This page shows a table contrasting the features of the text editors that interface to TeX .-Table of editor properties:- See also :* Comparison of word processors* Comparison of text editors...
.
Versions
LaTeX2e is the current version of LaTeX. , a future version called LaTeX3, started in the early 1990s, is still in development. Planned features include improved syntax, hyperlinkHyperlink
In computing, a hyperlink is a reference to data that the reader can directly follow, or that is followed automatically. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text with hyperlinks...
support, a new user interface, access to arbitrary fonts, and new documentation.
There are numerous commercial implementations of the entire TeX system. System vendors may add extra features like additional typeface
Typeface
In typography, a typeface is the artistic representation or interpretation of characters; it is the way the type looks. Each type is designed and there are thousands of different typefaces in existence, with new ones being developed constantly....
s and telephone support. LyX
LyX
LyX is a document processor following the self-coined "what you see is what you mean" paradigm , as opposed to the WYSIWYG ideas used by word processors...
is a free
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
, WYSIWYM
WYSIWYM
WYSIWYM is an acronym for What You See Is What You Mean, and refers to a paradigm for document editing...
visual document processor that uses LaTeX for a back-end. TeXmacs is a free
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
, WYSIWYG
WYSIWYG
WYSIWYG is an acronym for What You See Is What You Get. The term is used in computing to describe a system in which content displayed onscreen during editing appears in a form closely corresponding to its appearance when printed or displayed as a finished product...
editor with similar functionalities as LaTeX but a different typesetting engine. Other WYSIWYG editors that produce LaTeX include Scientific Word on MS Windows.
A number of TeX distributions are available, including TeX Live
TeX Live
TeX Live is a TeX distribution which is the replacement of its no-longer supported counterpart teTeX.It is now the default TeX distribution for several Linux distributions such as Fedora, Debian, Ubuntuand Gentoo....
(multiplatform), teTeX
TeTeX
teTeX is a TeX distribution for Unix-like systems. As of May 2006 teTeX is no longer actively maintained and its former maintainer Thomas Esser recommended TeX Live as the replacement....
(deprecated in favour of TeX Live, UNIX), fpTeX (deprecated), MiKTeX
MiKTeX
MiKTeX is a typesetting system for Microsoft Windows that is developed by Christian Schenk. It consists of an implementation of TeX and a set of related programs....
(Windows), proTeXt
ProTeXt
proTeXt is a freeware integrated development environment for LaTeX running on Microsoft Windows, developed by Thomas Feuerstack. Its most recent version is 3.0....
(Windows), MacTeX
MacTeX
MacTeX is a redistribution of TeX Live. While TeX Live is designed to be cross-platform , MacTeX includes Mac-specific utilities and front-ends...
(TeX Live with the addition of Mac specific programs), gwTeX (Mac OS X), OzTeX (Mac OS Classic), AmigaTeX (no longer available) Latexian (Mac OS X) and PasTeX (AmigaOS, available on the Aminet
Aminet
Aminet is the world's largest archive of Amiga-related software and files. Aminet was originally hosted by several universities' FTP sites, and is now available on CD-ROM and on the web.-History:...
repository).
Compatibility
LaTeX documents can only be shared with people who use Microsoft WordMicrosoft Word
Microsoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
or OpenOffice.org Writer
OpenOffice.org Writer
OpenOffice.org Writer is the word processor component of the OpenOffice.org software package. Writer is a word processor similar to Microsoft Word and Corel's WordPerfect, with some of their features....
by converting the LaTeX file (.tex) to Rich Text Format
Rich Text Format
The Rich Text Format is a proprietary document file format with published specification developed by Microsoft Corporation since 1987 for Microsoft products and for cross-platform document interchange....
(.rtf) or XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
. This can be done using the free software programs LaTeX2RTF
LaTeX2RTF
LaTeX2RTF is a translator program which is intended to convert a LaTeX document into the RTF format which can be imported by several text processors ....
or TeX4ht
TeX4ht
TeX4ht is a configurable converter capable of translating TeX and LaTeX documents to HTML and certain XML formats. Most notably, TeX4ht serves for converting TeX documents to formats used by word processors. It was developed by Eitan M...
.
See also
- AMS-LaTeXAMS-LaTeXAMS-LaTeX is a collection ofLaTeX document classes and packages developed for the American Mathematical Society . Its additions to LaTeX include the typesetting of multi-line and other mathematical statements, document classes, and fonts containing numerous mathematical symbols.It has largely...
- American Mathematical Society extension for LaTeX - BibTeXBibTeXBibTeX is reference management software for formatting lists of references. The BibTeX tool is typically used together with the LaTeX document preparation system...
reference management software typically used with LaTeX - Comparison of TeX editorsComparison of TeX editorsThis page shows a table contrasting the features of the text editors that interface to TeX .-Table of editor properties:- See also :* Comparison of word processors* Comparison of text editors...
- List of document markup languages
- REVTeXREVTeXREVTeX is a collection of LaTeX macros which is maintained anddistributed by the American Physical Society with auxiliary files and a user support guide, as part of a “REVTeX toolbox.” REVTeX is popular among scientists who submit papers to journals published by the American Physical Society , the...
- Publication Styles of the American Physical Society