What is Expressions: Definition and 331 Discussions

A regular expression (shortened as regex or regexp; also referred to as rational expression) is a sequence of characters that specifies a search pattern. Usually 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 theoretical computer science and 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, widely used, being the Perl syntax.
Regular expressions are used in search engines, search 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, as it has uses in many situations.

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  1. M

    LaTeX Paragraphing Latex expressions

    When I use Latex, the expression always comes out on a separate line. How do I keep the expression on the same line?
  2. binbagsss

    Tensor Covariant Derivative Expressions Algebra (Fermi- Walk

    Homework Statement Hi I am looking at part a). Homework Equations below The Attempt at a Solution I can follow the solution once I agree that ## A^u U_u =0 ##. However I don't understand this. So in terms of the notation ( ) brackets denote the symmetrized summation and the [ ] the...
  3. M

    MHB Evaluating Trigonometric Expressions

    Given h(x) = tan x, evaluate dh/dx on [pi/4, 1]. Note: d = delta I need one or two hints. I can then try on my own.
  4. opus

    Using Power Reducing Formulas to rewrite Trig Expressions

    Homework Statement Use the power reducing formulas to rewrite the expression that does not contain trigonometric functions of power greater than 1. Given expression: ##4sin^2xcos^2x## 2. Homework Equations Relevant Power-Reducing Formulas: ##sin^2x=\frac{1-cos2x}{2}##...
  5. Tunalover

    LaTeX Discover LaTex & MathJax for Writing Math Expressions

    Until this forum I had never heard of LaTex for writing mathematical expressions. Can anyone help me: A. find out where to download these programs. B. find someone who would be willing to provide guidance on installing and using these programs C. find LaTex and MathJax primers I can print...
  6. H

    I Correct notation for some functional expressions

    Having some trouble determining the most mathematically correct way to express something I understand only numerically and physically. Basically I am modeling radiation within a volume. 1. For each point dV within a volume V there is a scalar value e(dV), which is an amount of radiation emitted...
  7. Monoxdifly

    MHB [ASK] Math Type in MS Word - Expressions Problematic

    I have Math Type 6.9 in my computer and everyone of my coworkers has it but there's a problem with mine. Sometimes when I've been working for hours, the math expression I copied from Math Type couldn't get pasted to Microsoft Word (I tried the Save option via Math Type plugin too, and when the...
  8. Richie Smash

    Calculate the height of a water column and expressions for P

    Homework Statement The apparatus shown may be used to determine the density of an unknown liquid X. The tube has a uniform cross section and the height of the water column is twice that of Liquid X. A and B are the same horizontal level. The pressure difference between points A and C is...
  9. F

    B Simplifying expressions -- What exactly does it mean to simplify an expression?

    What exactly does it mean to simplify an expression. I understand that an expression becomes more simple when you combine like terms but what other conditions are there? Is x(5x+1) more or less simple than 5x^2 +x? Do square roots need to be moved to the numerator?
  10. P

    Rational expressions and domains

    Homework Statement Okay, I have two examples that are confusing me. I am not sure where all the numbers that must be excluded from the denominators so that we're not dividing by zero are coming from. a) x2 + 6x +5 / x2 - 25 b) x-7 / x-1 multiplied by x2-1 / 3x-21 Homework Equations None...
  11. Boudy

    I Need Aproximate expressions for : ln(x) and 1/ln(x) Thanks

    Hi there: I am looking for approximate expressions for the two functions: ln(x) and 1/ln(x) . Any help? Thanks in advance.
  12. Z

    MHB ZyBooks: 2.4.1: Enter the output of the integer expressions.

    I'm not sure how to do these problems here. Help me learn them please!
  13. D

    Matlab expressions for two types of odd polynomials

    Homework Statement i am trying to find the expressions for the "equiripple" and "maximal flat" polynomials for the equiripple :[/B] for maximal flat: Homework EquationsThe Attempt at a Solution i know that for maximal flat its butterworth polinomials, but for P_3 i don't get the same...
  14. P

    Showing equivalent potential expressions for a Transverse String

    Homework Statement I'm going through the derivation here starting on page 16. This image adds some context: . Generalizing their result to the i'th particle they find the extended distance between two masses being ##\Delta l= \frac{(y_i-y_{i-1})^2}{2a}## Then since the potential energy is...
  15. D

    MHB Using constants in expressions.

    import java.util.Scanner; public class ShippingCalculator { public static void main (String [] args) { int shipWeightPounds = 10; int shipCostCents = 0; final int FLAT_FEE_CENTS = 75; shipWeightPound = shipCostCost / shipWeightPound; final int CENTS_PER_POUND...
  16. J

    MHB Algebraic Rational Expressions

    I am attempting to find the solution to the following question. Simplify and state the restrictions on the variables\frac{5a^5b^6}{10a^2b^3}\div\frac{2a^4b^2}{20a^3b^5} Not really understanding how to find the restrictions with these set variables.
  17. Sollicitans

    Calculating events from phrasal expressions

    Homework Statement This excresice is supposed to help you understand the basic operations of sets, later used in probability. I am given the following phrases and have to write them in using mathematics. Given three events A, B and C, which belong to sample space S, calculate the following...
  18. K

    B Expressions of ##log(a+b), tan^{-1}(a+b),sin^{-1}(a+b)##,etc

    Hi, I got these: $$log(a+b)\approx \frac{b*logb-a*loga}{b-a} + log2 -1$$ $$tan^{-1}(a+b)\approx \frac{b*tan^{-1}2b-a*tan^{-1}2a+\frac{1}{4}*ln\frac{1+4a^2}{1+4b^2}}{b-a}$$ $$sin^{-1}(a+b)\approx \frac{b*sin^{-1}2b-a*sin^{-1}2a+\frac{1}{2}*(\sqrt{1-4b^2}-\sqrt{1-4a^2}}{b-a}$$ And, similarly for...
  19. Charles Henderson

    Boolean Algebra - Simplifying to two different expressions

    For the expression: (B and C) or (not B and not C) or (A and (not B) and not C) I get two different answers depending on the order I do the simplification. 1. If I factor C out of the first and third terms I get (B and C) or (A and C) or (not B and not C) 2. If I factor not B out of the...
  20. K

    MHB Deriving expressions using double angle formula?

    How do I use the double angle identity in order to derive this expression: cos6(u)?
  21. Unteroffizier

    Algebra II, Rational Expressions & Square Roots problems

    Problem 1 Simplify/solve: 2*81/2-7*181/2+5*721/2-50 Attempt at solution: a1/2=√a ⇒ 2*√8 - 7*√18 + 5*√72 - 50 = 2√8 - 7√18 + 5√72 - 50 = ? Do not know how to proceed beyond this point. Have experimented with little luck. Problem 2 Simplify/solve: a-1(1+1/a2)-1/2 * (1+a2)1/2 Attempt at...
  22. V

    Equivalent Expression for cot(-π/4) in Terms of Acute Angle

    Homework Statement State an equivalent expression in terms of the related acute angle? (A) cot(-π/4) Homework EquationsThe Attempt at a Solution (A) I made the the unit circle and since its negative I went clockwise and made it into the fourth quadrant. I ended up getting -cotπ/4. However...
  23. T

    I Equivalence of two complex expressions

    I found the above while going through my textbook, where the textbook was trying to explain that the principal value of the product of two complex numbers raised to an exponent is not necessarily equivalent to the product of the two complex number each raised to the same exponent first. Based...
  24. moenste

    Flux density expressions at solenoid centre

    Homework Statement A long air-cored solenoid has two windings wound on top of each other. Each has N turns per metre and resistance R. Deduce expressions for the flux density at the centre of the selenoid when the windings are connected (a) in series, and (b) in parallel, to a battery of EMF E...
  25. L

    Doublecheck reduction of rational expressions

    Homework Statement teacher gave me the correct solution which said that the result from him was as follows ##\frac{1}{a^2b^6}## Homework Equations original problem was as follows ##\frac{ (\frac{1}{a})^2*b^{-3}}{ ab^3 }## The Attempt at a Solution...
  26. saybrook1

    A Intensive vs Extensive Expressions

    Hello guys, I'm struggling to understand why some expressions are deemed to be extensive(or particularly extensive for that matter) and others are not. As far as I understand, extensive properties are physical quantities whose magnitude is additive for subsystems and this magnitude is...
  27. E

    Algebraic expressions for the amount of time that elapses

    Homework Statement A single gas molecule of inertia m is trapped in a box and travels back and forth with constant speed v between opposite walls A and B a distance l apart. At each collision with a wall, the molecule reverses direction without changing speed.Write algebraic expressions for the...
  28. How to evaluate an expression with variables | Introduction to algebra | Algebra I | Khan Academy

    How to evaluate an expression with variables | Introduction to algebra | Algebra I | Khan Academy

    Learn how to evaluate an expression with variables using a technique called substitution (or "plugging in"). Watch the next lesson: https://www.khanacademy.o...
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  29. How to evaluate expressions with two variables | 6th grade | Khan Academy

    How to evaluate expressions with two variables | 6th grade | Khan Academy

    We've done a few examples together where we were faced with 1 variable. Why not try one that has 2 variables? Practice this lesson yourself on KhanAcademy.or...
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  30. How to evaluate expressions in two variables with decimals and fractions | 6th grade | Khan Academy

    How to evaluate expressions in two variables with decimals and fractions | 6th grade | Khan Academy

    Learn how to evaluate expressions that have two different variables in them by using a technique called substitution (or "plugging in"). Practice this lesson...
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  31. How to evaluate an expression using substitution | Algebra I | Khan Academy

    How to evaluate an expression using substitution | Algebra I | Khan Academy

    In this example we have a formula for converting Celsius temperature to Fahrenheit. Let's substitute the variable with a value (Celsius temp) to get the degr...
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  32. Evaluating an algebraic expression with exponents | 6th grade | Khan Academy

    Evaluating an algebraic expression with exponents | 6th grade | Khan Academy

    We're going to put our order of operations knowledge to work as we evaluate this expression. Exponents, specifically, are our focus here. Watch the next less...
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  33. How to write basic expressions with variables | 6th grade | Khan Academy

    How to write basic expressions with variables | 6th grade | Khan Academy

    Learn how to write basic algebraic expressions. Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/cc-sixth-grade-m...
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  34. How to write expressions with variables | Introduction to algebra | Algebra I | Khan Academy

    How to write expressions with variables | Introduction to algebra | Algebra I | Khan Academy

    Learn how to write simple algebraic expressions. Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/algebra/introdu...
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  35. How to write algebraic expressions with parentheses | Algebra I | Khan Academy

    How to write algebraic expressions with parentheses | Algebra I | Khan Academy

    Learn how to write algebraic expressions that involve grouping quantities in parentheses. Practice this lesson yourself on KhanAcademy.org right now: https:/...
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  36. How to find equivalent expressions by combining like terms and using the distributive property

    How to find equivalent expressions by combining like terms and using the distributive property

    "Equivalent algebraic expressions exercise Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/cc-sixth-grade-math/c...
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  37. J

    I Relating integral expressions for Euler's constant

    Euler's constant is defined as ##\gamma = \lim_{n \rightarrow \infty} \left( 1 + {1 \over 2} + {1 \over 3} + \cdots + {1 \over n} - \ln n \right)##. This can be easily represented as an integral: ## \gamma = \int_0^\infty \left( {1 \over 1 - e^{-x}} - {1 \over x} \right) e^{-x} dx \qquad Eq.1...
  38. snoopies622

    I Exactly why are these two expressions similar?

    So if angular momentum L = m r^2 \dot {\theta} and we take the first time derivative \frac {d}{dt} L = 2mr \dot {r} \dot {\theta} + m r^2 \ddot {\theta} the first term looks similar to the Coriolis force 2m( \bf {v} x \bf { \dot {\theta} } ) but I can't figure out why. Of course...
  39. P

    Vector Expressions Homework: Evaluate 1-8

    Homework Statement let ##\vec{r}## be a vector from origin to the point (x,y,z) and let ##{\vec{r}\,}'## be a vector from the origin to the point (x',y',z'). Evaluate the following expressions ##1. \triangledown r ## ##2.\triangledown\frac{1}{r}## ##3.\triangledown\cdot r##...
  40. JuanC97

    I Why Does Integrating |f(x)| Differ from Integrating f(x)?

    I know that \sqrt{f(x)^2} = |f(x)| However... I've just noticed that integrals of expressions like this are usually assumed to be equal to the integral of f(x) without the absolute value. I'd like to know how that's possible. Is weird for me to consider those expressions; specially because of...
  41. leighflix

    B Factoring algebraic expressions contaning fractions

    http://imgur.com/RNsBBoO (image) Can someone elaborate as to how he factored this? The textbook provided nothing else about factoring algebraic expressions with fractions than this image.It avoided fractions in factoring like a plague I guess. I understand the 3rd step to put the (x + 1)^(3/4)...
  42. N

    MHB Translating to algebraic expressions

    I am not able to express it symbolically I need your assistance. Thanks! A room is $p$ ft. Long and $x$ yards in width; how many yards of carpet two ft. Wide will be required for the floor?
  43. S

    Regular expressions with google web search

    Hi all, Cam google web search accepet regular expressions? Especially, I need to search strings with any number between two words, for example: "vehicle runs at XXX km/h". Thank you
  44. R

    MHB Order of operations to simplify expressions .

    Hi, I have worked the problem but I am not sure that this is the correct answer, Please help. 3(-3) - (5)2^2 ____________ 8- SQRoot(36) +12 I got an answer of 11/14 but When I check on an online calculator to see if it is correct I am getting 5.5 ... 2^2 = TWO SQUARED SQRoot = Square...
  45. N

    MHB Symmetry in the algebraic expressions

    Hello! I read about the symmetry of the following product $(x+a+b)(x+b+c)(x+c+a)$ my book says that a, b and c occur symmetrically. Why is that?
  46. 3301

    Expand powers of binomial expressions

    Homework Statement The problem comes in second term after 4(2z...) Homework EquationsThe Attempt at a Solution so i got 4 (8z^3) 5k. 32 (z^3) * (20k). After that i left it like that but I supposed to get answer like this 160 z^3 * k I can conjoin constants of z and k variables? Or am I...
  47. Greg Bernhardt

    Are You Up for a Regular Expressions Crossword Challenge?

  48. M

    Analytical Expressions for Frequency Response

    Hi, I am struggling to understand the maths in the text shown below. (1) How does: r(t) = Acos(wt)+Bsin(wt) become; sqrt((A^2)+(B^2))cos(wt - arctan(B/A))? (2) He states that we can represent the input as a phasor and in one of three ways but doesn't say which one. (3) He then focus on the...
  49. S

    MHB Rational Expressions: Subtract 1/2x-7/x-3

    1/2x-7/x-3 Subtract
  50. L

    Signed and unsigned integer expressions?

    So I just completed a simple exercise that converts all letters of a string to upper case letters. The program works but it comes with the warning: comparison between signed and unsigned integer expressions [Wsign-compare]. What does this mean? While whatever is causing the warning does not seem...
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