Regular expression

A regular expression, regex or regexp is a sequence of characters that define a search pattern. Such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation, it is a technique developed in formal language theory. The concept arose in the 1950s when the American mathematician Stephen Cole Kleene formalized the description of a regular language; the concept came into common use with Unix text-processing utilities. Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another used, being the Perl syntax. Regular expressions are used in search engines and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK and in lexical analysis. Many programming languages provide regex capabilities either built-in or via libraries; the phrase regular expressions called regexes, is used to mean the specific, standard textual syntax for representing patterns for matching text, as distinct from the mathematical notation described below.

Each character in a regular expression is either a metacharacter, having a special meaning, or a regular character that has a literal meaning. For example, in the regex a. A is a literal character which matches just'a', while'.' is a metacharacter that matches every character except a newline. Therefore, this regex matches, for example,'a', or'ax', or'a0'. Together and literal characters can be used to identify text of a given pattern, or process a number of instances of it. Pattern matches may vary from a precise equality to a general similarity, as controlled by the metacharacters. For example. Is a general pattern, is less general and a is a precise pattern; the metacharacter syntax is designed to represent prescribed targets in a concise and flexible way to direct the automation of text processing of a variety of input data, in a form easy to type using a standard ASCII keyboard. A simple case of a regular expression in this syntax is to locate a word spelled two different ways in a text editor, the regular expression serialie matches both "serialise" and "serialize".

Wildcards achieve this, but are more limited in what they can pattern, as they have fewer metacharacters and a simple language-base. The usual context of wildcard characters is in globbing similar names in a list of files, whereas regexes are employed in applications that pattern-match text strings in general. For example, the regex ^+|+$ matches excess whitespace at the beginning or end of a line. An advanced regular expression that matches any numeral is??. A regex processor translates a regular expression in the above syntax into an internal representation which can be executed and matched against a string representing the text being searched in. One possible approach is the Thompson's construction algorithm to construct a nondeterministic finite automaton, made deterministic and the resulting deterministic finite automaton is run on the target text string to recognize substrings that match the regular expression; the picture shows the NFA scheme N obtained from the regular expression s*, where s denotes a simpler regular expression in turn, recursively translated to the NFA N.

Regular expressions originated in 1951, when mathematician Stephen Cole Kleene described regular languages using his mathematical notation called regular events. These arose in theoretical computer science, in the subfields of automata theory and the description and classification of formal languages. Other early implementations of pattern matching include the SNOBOL language, which did not use regular expressions, but instead its own pattern matching constructs. Regular expressions entered popular use from 1968 in two uses: pattern matching in a text editor and lexical analysis in a compiler. Among the first appearances of regular expressions in program form was when Ken Thompson built Kleene's notation into the editor QED as a means to match patterns in text files. For speed, Thompson implemented regular expression matching by just-in-time compilation to IBM 7094 code on the Compatible Time-Sharing System, an important early example of JIT compilation, he added this capability to the Unix editor ed, which led to the popular search tool grep's use of regular expressions.

Around the same time when Thompson developed QED, a group of researchers including Douglas T. Ross implemented a tool based on regular expressions, used for lexical analysis in compiler design. Many variations of these original forms of regular expressions were used in Unix programs at Bell Labs in the 1970s, including vi, sed, AWK, expr, in other programs such as Emacs. Regexes were subsequently adopted by a wide range of programs, with these early forms standardized in the POSIX.2 standard in 1992. In the 1980s the more complicated regexes arose in Perl, which derived from a regex library written by Henry Spencer, who wrote an implementation of Advanced Regular Expressions for Tcl; the Tcl library is a hybrid NFA/DFA implementation with improved performance characteristics. Software projects that have adopted Spencer's Tcl regular expression implementation include PostgreSQL. Perl expanded on Spencer's origi

Phyllis Reid Fenner

Phyllis R. Fenner was an American librarian, author and storyteller, she was a long-term companion of Clara Sipprell. Phyllis Fenner, born in Almond, New York on October 24, 1899, was the daughter of Viola Victoria Van Orman Fenner and William Lavern Fenner, a merchant, her grandfather ran a general store in her hometown, which became the subject of her article "Grandfather's Store", published in the Reader's Digest in 1942. She graduated from Almond High School, from Mount Holyoke College in 1921, she received a degree in library science from Columbia University in 1934, she studied at the New York University School of Retailing. Fenner worked in Brooklyn at Loeser's Department Store, in Connecticut as a social caseworker, in Virginia as a private school teacher. Beginning in 1923, Fenner was a librarian at Plandome Road School in New York. While there, she created what she considered the ideal type of library, among the various types of libraries that she identified and wrote about, called the Unlimited Service Library.

She believed that librarians should see themselves as teachers, not just custodians of books, believed in creating environments where students wanted to come to explore books. She did this through storytelling, giving talks, using games to encourage participation, leading various clubs, making the library a comfortable place to visit, she was quoted in the Library Journal in 1954 as having said that "… we will do most anything in my library, because I believe that if the library is to serve, it must bring children and books together joyfully." She retired there in 1955. At St. John's University in Brooklyn, she taught a course in storytelling. Fenner was a public speaker about library science, she wrote one of the first books about elementary school libraries, Our Library, which received positive reviews from Time magazine and The New York Times Book Review. In 1945, she published The Library in the Elementary School: A Searching Discussion of Activities and Possibilities. In 1957, she published Proof of the Pudding: What Children Read.

She published 34 young adult anthologies, including There Was a Horse, Stories from Folklore, exhibited at the Metropolitan Museum of Art for its quality illustrations. She wrote for Reader's Digest, reviewed books for Instructor, was on the editorial board of Cademus Books Weekly Reader Club, on the advisory board of Story Parade Magazine, she was a member of the American Library Association, Progressive Education Association, New York State Teachers Association, Women's National Book Association, Pen & Brush. Sipprell and Fenner met in 1937, when Sipprell moved to Vermont. In the 1960s, they had a house built by Harold Olmstead. After retiring from her work as a librarian, Fenner moved permanently to Manchester, she traveled extensively with Sipprell, who died in 1975. She asked for her ashes to be buried on a rock atop Manchester. Fenner was sick for many years before her death on February 26, 1982. Documents by and about Fenner are archived at the Williston Memorial Library at Mount Holyoke College.

Edwin L. Bigelow. Manchester, Vermont, 1761-1961: A Pleasant Land Among the Mountains. Town of Manchester. Pp. 260, 310. Mary Hard Bort. Manchester: Memories of a Mountain Valley. Manchester Historical Society. P. 113. Phyllis R. Fenner, books at the Library of Congress

Sarada K. Sarma

Sarada Kanta Sarma is a geotechnical engineer, emeritus reader of engineering seismology and senior research investigator at Imperial College London. He has developed a method of seismic slope stability analysis, named after him, the Sarma method. Sarma was educated in India, studying civil engineering at the Indian Institute of Technology in Kharagpur and geotechnical engineering at Imperial College specialising in earthquake engineering and engineering seismology, he worked under the supervision of professor Nicolas Ambraseys and obtained his PhD degree in 1968. His thesis title was "Response characteristics and stability of earth dams during strong earthquakes", he joined the staff in 1967 as a Lecturer in Engineering Seismology. His major research focuses on engineering geotechnical engineering, he specialised in seismic analysis and performance of soil slopes, earth dams and the earthquake resistant design of foundations and design code development and evaluation. He developed a new method of analysing the stability of slopes and dams in seismic conditions and calculating the permanent displacements due to strong shaking.

This method, published in the 1970s is named after him and it is a special case of a Limit Equilibrium method of geotechnical analysis. It has been extensively used in seismic analysis software for many years, although nowadays modern finite element analysis software are more used for special case studies; the Sarma method is called an advanced and rigorous method of static and seismic slope stability analysis. It is called advanced; the multi-wedge approach allows for non-vertical slices and irregular slope geometry. It is called a rigorous method because it can satisfy all the three conditions of equilibrium and vertical forces and moments; the Sarma method is nowadays used as a verification to finite element programs and it is the standard method used for seismic analysis. In recognition of his contribution to earthquake engineering, he has been awarded a number of awards and has been invited to give lectures, serve the academic advisory board of several conferences and provide consulting work and advice for various dam projects.

Sarma retired from Imperial College in 2004. Slope stability Imperial College Civil & Environmental Engineering Sarada K Sarma