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. R

    Basics of quintic and quadratic expressions

    <b>I need a brain refresher</b> to see if i have everything straight in quintic and quadratic expressions. The n's in an expression represents how many turns a line would have The amount of (x+1)^2 means a quadratic curve The if the n is odd there are no complex roots Now here is the...
  2. E

    Expressions used in change of variables

    Hi. I know the title is not very informative. Here's what I'm trying to do: I have f(x,y). I want to perform a change of variables to obtain a pre-defined g(u,v). How can I work out the actual expressions u(x,y) and v(x,y) so that it works out (including the Jacobian as well)? I have a...
  3. M

    How Are Radical Expressions Applied in Professional Fields?

    I have a project in which I need to write a paper on how radical expressions are used in careers. I can think of plenty of careers that use radical expressions, the problem is, no matter how much I research I can't find anything on <i>how</i> they are used. I have tried to find mathematics of...
  4. B

    Expressions for energy in 1d well

    Question states: Derive an expression for the energy of the bound states of a particle in the one-dimensional well defined by: V(x) = \infinity x<=0 (Region I) V(x) = 0 0<x<L (Region II) V(x) = V_0 x>=L (Region III) And its not been too bad. Up until a point. I know for I \psi(x)=0. In...
  5. T

    Find Inverse of y=(x)^(1/3) & y=3(2)^x

    yea ok but wait how do u find the inverse of like y=(x)^(1/3) y=3(2)^x whats the formula is not in the book BTW i can't do those equations in latex...
  6. M

    How do I rationalize the numerator in this expression?

    The question states Rationalize each of the following numerators to obtain and equivalent expression. (sqroot(h^2+5h+4) -2 ) / h How do i rationalize the numerator here. I don't remember thanks
  7. P

    Need Help with Simplifying Expressions on Your Graphing Calculator?

    {(m^2 +2m -3)/(m^2-4)} / {(m^2 - 2m +1)/(m^2 -1) = {(m^2 +2m -3)/(m^2-4)} x {((m(m-1))/ (m^2 -2m +1)} = [(m+3)m] / [(m +2)(m-2)] does that like rightish? any opinions will be appreciated! ~Amy
  8. S

    Prove the expressions by induction method

    hey guys 1st week of my university and i got the painful assignment. I've not touched math from last 4-5 months, so I'm having trouble with few questions. Please help me out, thanks in advance 1- Prove that if x not equal 0, then x + 2x^{2} + 3x^{3} + ... + nx^{n}(1+x) = [ x - (n - 1)x^{n+1}...
  9. E

    How to Create a Regular Expression for Strings with an Odd Number of Zeroes?

    How do I approach this problem? give a regular expression for a set containing strings consisting of 0s and 1s where numbr of zeroes is odd... thanks ps: I have tried it with Kleene's theorem, but there is so many possibilities that i get lost
  10. L

    Maths problem: deriving expressions for the critical temperature/volume/pressure

    I have to show that for a van der Waals gas the critical temperature, volume and pressure are given by: T_c= \frac{8a}{27bR} V_c= 3nb p_c= \frac{a}{27b^2} I started off this way: Van der Waals states that for a non ideal gas the pressure is: P = \frac{nRT}{V-nb} - a...
  11. JasonRox

    Java Creating a Prime Sieve with Boolean Expressions

    I'm trying to create a sieve (prime sieve). A nice quick simple one using boolean expressions. I remember on Visual Basics it began by creating like X number of boolean variables and then sieve them out by classifying them as false... and so on. How to a create a large group of boolean...
  12. W

    Multiplying Rational Expressions

    This is a question I have to do for tomorrow \frac{1+4x+4x^2}{x}\times\frac{3x^4}{12x^2-3}. I just factor the tops and then cancel where I can. This is what I came up with: \frac{3x^4}{12x^3-3x} But the answer key says: \frac{x^3(1+2x)}{2x-1} What have I done wrong?
  13. M

    Understanding Grammar #2: Ambiguity, Elimination, and Boolean Expressions

    what langugage?? grammar #1: S->(L)|a L->L,S|S what language does this grammar generate? some strings generated by this grammar r (a,a), (a,(a,a))... grammmar #2: bexpr->bexpr or bterm| bterm bterm-> bterm and bfactor| bfactor bfactor-> not bfactor| (bexpr) | true | false is...
  14. M

    Proving Matrix Expressions: AX = XA

    Hi I got a question regarding a matrix expression: Let X \in Mat_{n,n} (\mathbf{F}) . Then I'm suppose to show AX = XA for all A \in Mat_{n,n} \mathbf{(F)} if and only if s \in \mathbf{F} What is the best way of going about this? /Fred
  15. A

    Multiply and Divide Rational Expressions

    I thought I knew what I was doing (because I've done this before) but I can't see what's happening in this one example...I understood what was going on right up until the last step. If you are dividing two rational expressions, flip the second expression and multiply the two rational...
  16. R

    Cantor Expressions: Solving A-F (2,7,19,87,1000,1M)

    What is the cantor expansion of: A. 2 B. 7 C. 19 D. 87 E. 1000 F. 1,000,000 The algorithm to solve these small problems is the most difficult for me. The algorithm that I came up with states: Asub(n) N! + Asub(n-1) (n-1)! +...+ Asub(2)2! + Asub(1)1!, where Asub1 is an integer with...
  17. M

    Mastering Rational Expressions: Simple Tips and Tricks for Advanced Math Classes

    Right now in math class we are learning rational expressions. Since I am in an advanced math class, it seems like we learn a new lesson everyday. So if you don't understand something, you pretty much need to teach yourself. I don't really understand rational expressions, so can someone tell...
  18. S

    Rational Expressions Answers: Check Your Work

    I was wondering if someone could check these questions to make sure that I am doing these correctly. I have attached a few questions in word document as I could not type it properly on here.
  19. R

    Evaluate Powers Expressions: (4/9)^(3/2) and (-27)^(-1/3)

    Evalulate, leaving the answer as a fraction: a) \left(\frac{4}{9}\right)^\frac{3}{2} b) (-27)^-^\frac{1}{3} Please Help. Thanks
  20. A

    Help Me Prove Two Expressions Equal: Can You?

    hi i have a small problem. i need to prove that these two expressions are equal : (n*Sum{i=1,n}Xi*Yi - Sum{i=1,n}Xi*Sum{i=1,n}Yi)/(n*Sum{i=1,n}(Xi)^2 - (Sum{i=1,n}Xi)^2) and the expression : (Sum{i=1,n}(Xi)*(Xi*Y^ - Yi*X^))/(Sum{i=1,n}((Xi)^2 - (x^)^2 )) here is x^ and y^ the...
  21. W

    Question in regards to the equilibrium law and expressions

    Considering the following equilibrium reaction A(g) \longleftrightarrow 2B(g) + C(g) And the question: When 1.00 mol of A is placed in a 4.00 L container at temperature t, the concentration of C at equilibrium is 0.050 mol/L. What is the equilibrium constant for the reaction at...
  22. D

    Calculating Decimals for Expressions

    can somebody tell me how many decimals places for this question and tell me if i am doing this right 1. Calculate a value for the expression p=a^-2 a=27.3 +- 0.05 metres ( the plus and minus symbol is on top of each other) b) calculate the maximum error in your answer this...
  23. D

    When find LCD for a rational expressions.

    Ok I have to find the Lowest Common Denominator for 3 ration expressions. I don't think the numerators are important so Ill just leave them out. The denominators are x^2 - 4 and x -2 I got the LCD as x-2. correct? When finding the LCD in expressions like this you just have to factor...
  24. R

    Bilinear Expressions in Quantum Field Theory: Benefits & Uses

    Hi all, Doing a graduate QFT course. We've been looking at the bilinear expressions involving the adjoint spinor and the gamma matrices and how the various combinations transform as scalars, vectors etc. My question is this: Other than just appreciating the fact that various...
  25. Gamma

    Mathematica How to write mathematical expressions?

    Can anyone tell me how I can write mathematical expressions here. I read the 'LateX crash course'. See what happens. [tex] a^2 + b = sqrt {c}[\tex] What am I doing wrong? regards, Gamma.
  26. V

    Expressions with (6/x+2) + (8/x+3)

    If i have something like (6/x+2) + (8/x+3) how to i do that? aren't i supposed to invert and multiply or something, thanks --Val
  27. A

    Rational Expressions loooong BUT NEED HELP

    state the vertical asymptote(s), x-intercept(s), y-intercept(s), domain and range of f(x)=(1)/(4x^2)-1 ok I factored the denominator and got (2x+1) (2x-1) I solved for x, so the x-intercepts are x=-1/2, and x=1/2 for only (4x^2)-1 the reciprocal function has no x-intercepts. Sub in x=0 to...
  28. A

    Simplify conjugate expressions

    1) (-7+20)(-10-3i) 2) (-2-5i)/(3+4i) I don't think I did these two questions right does anyone know how?
  29. exequor

    Program for writing equations / expressions

    just like there is a coding to write proper equations in this forum does anyone know a computer program that can do the same so that i can implement it into word documents?
  30. N

    LaTeX Finding the Best LaTeX Editor for WYSIWYG and Math Expressions

    Hi everybody! I'm looking for a good \LaTeX editor... I'm primarily looking for an application where text and styles are WYSIWYG, but mathematical expressions are written using latex. I tried LyX, but didn't really like the one... I'm currently using TeXnicCenter, which has a few to many bugs...
  31. J

    Understanding Expressions like SU(2), O(3) and E(8)

    Could some one please explain to me, in the simplest way possible and withought lots of mathematical jargon, what expressions such as SU(2), O(3), E(8) etc. mean? I think they all have something to do with rotation (although I could be completely wrong). Thanks.
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