What is Domain: Definition and 741 Discussions

A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name identifies a network domain, or it represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a website, or the web site itself or any other service communicated via the Internet. In 2017, 330.6 million domain names had been registered.Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name. Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, info, net, edu, and org, and the country code top-level domains (ccTLDs). Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
The registration of these domain names is usually administered by domain name registrars who sell their services to the public.
A fully qualified domain name (FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Traditionally a FQDN ends in a dot (.) to denote the top of the DNS tree. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.

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  1. R

    Why is the domain of this rational function restricted to x > 0?

    When I plot y = 3x^{\frac{4}{3}}-\frac{3}{32}x^{\frac{2}{3}}, I get: https://dl.dropbox.com/u/5653705/pfgraph1.png but I don't see any reason for the domain to be restricted to x > 0 . There is only a cubic root, which is well defined for negative numbers ... I've tried on a few...
  2. C

    MHB Domain of the function of two variables

    Hi, I'm studying Calculus 2 now, and I am a litle bit confused in this question. 1- Determine and plot the domain of the function of two variables a) f(x,y)=\sqrt[]{1+x^{2}+y^{2}} x^{2}+y^{2}\geq -1 doing x^{2}+y^{2}= -1 i guess this is the graph of Hyperbole, but my teacher said is a...
  3. K

    What's negative frequency in analysis of s domain and w domain

    what's negative frequency? can we say s=-3 in example bode plot ! or we can say it's unstable at w=-3 rad/s that's I mean is there negative frequency??
  4. P

    Composite system, rigged Hilbert space, bounded unbounded operator, CSCO, domain

    Is something wrong in my assertions below? Suppose we have two quantum systems N and X. Let N is described by discrete observable \hat{n} (bounded s.a. operator with discrete infinite spectrum) with eigenvectors |n\rangle. Let X is described by continuous observable \hat{x} (unbounded s.a...
  5. A

    Express through basic quantifiers on the given domain:

    Homework Statement x is square free (not divisible by a perfect square) on Z Homework Equations Z meaning all integers. The Attempt at a Solution I did a similar problem earlier that asked for the expression for prime numbers on the Natural numbers domain. For that problem the...
  6. P

    Rigged Hilbert space, separable space, domain of CSCO, mapping

    Suppose that we have rigged Gilbert space Ω\subsetH\subsetΩ\times (H is infinite-dimensional and separable). Is the Ω a separable space? Is the Ω\times a separable space? Consider the complete set of commuting observables (CSCO) which contain both bounded and unbounded operators...
  7. B

    Domain of validity of classical electrodynamics

    i am currently reading griffith's book on electrodynamics, though he does an excellent job with the theory (along with all the sloppiness in math) he does not really answer the question, how well does this theory apply to the real world. i know Newton's theory is valid at v<<c, however in...
  8. C

    Find the domain of this function

    What is the domain of sqrt(2x-x^3) I thought this would be pretty straight forward but I am completely stumped. So obviously square root is not defined for (-inf, 0), therefore I said: 2x-x^3 >= 0 Working this out you get x <= sqrt(2) as the domain. That is partially correct but I can't for...
  9. S

    Plot frquency resonse from transfer function in complex frequency domain

    I am going through a past paper for an upcoming exam and I want to check that I am approaching this question correctly. H(s) = 1/(s2 + 8485.28s + 36x10-6) Calculate and plot frequency response for 0 rad/s, 500 rad/s, 1000 rad/s and 10000 rad/s. I am under the impression that the 's'...
  10. nomadreid

    Second-order variables: elements of domain only without quantifiers?

    On one side one can define second-order variables as ranging over all elements of Pk(M) for all natural numbers k (P=power set of M, M is the universe of the model, superscript being iteration). On the other side it is sometimes defined as ranging over all first-order relations and predicates...
  11. A

    Why isn't R a domain for \frac{1}{2}(a+b\sqrt{2})?

    Homework Statement If we have R = \{ \frac{1}{2}(a+b\sqrt{2}) \}. Homework Equations The Attempt at a Solution For the identity, we have a=2 and b=0. So the identity is not equal to zero. Also, there can't be any zero divisors, because...
  12. T

    A mapping from an integral domain to non-negative integers, Abstract Algebra

    So just had this question as extra credit on a final: Let D be an integral domain, and suppose f is a non-constant map from D to the non-negative integers, with f(xy) = f(x)f(y). Show that if a has an inverse in D, f(a) = 1. Couldn't figure it out in time. I was thinking the way to go...
  13. B

    Domain Differentiation question

    if a function f is differentiable of [0,2pi] can I integrate its derivative df on [-pi, pi]?
  14. F

    Convolution in Frequency Domain

    Homework Statement Find the Fourier transform of the following signal JUST by using the FT table and the FT properties x(t) = sin(t) -pi<=t<=pi 0 otherwise NOTE: I am using CONVOLVED WITH as a substitute for * (the real convolution operator) because I cannot express...
  15. P

    Looking for a Free Domain Coloring Grapher?

    Hey guys, Does anyone know of a good, free domain coloring grapher? I can't find a decent one anywhere.
  16. O

    MHB Conditions for integral domain to be a PID

    Let R be an integral domain. Then R is a PID if the following 2 conditions hold: 1) any 2 elements a, b \in R have a greatest common divisor which can be written as ra + sb for some r, s \in R . 2) If a_1, a_2, ... are nonzero elements of R such that a_{i+1}|a_i for all i, then there is...
  17. N

    Using Node-Voltage method in the phasor domain

    I was wondering if there is an easier way to solve circuits using matrix inversion if I have complex numbers. So far I've been doing them by hand with 2x2 matrices. It isn't hard, but it takes a while. I have a test coming up in about a week which will have 10 questions that have to be solved in...
  18. P

    Integrating out of the real domain of a function

    Check this out: \int_{-1}^{0} ln(x) dx u=ln(x), dv=dx du=\frac{1}{x},v=x \int_{-1}^{0} ln(x) dx= x\space ln(x) \|_{-1}^{0} -\int_{-1}^{0} \frac{x}{x} dx =x\space ln(x) \|_{-1}^{0}-x \|_{-1}^{0} =\lim_{x\to0} x\space ln(x)-(-ln(-1))-(0-(-1)) \lim_{x\to0} x\space ln(x)=lim_{x\to0}...
  19. Barnak

    Interpretation of the integration domain symbol

    I'm having an interpretation problem with the notation used in physics, under the integration sign. What is the proper interpretation of the domain of integration symbol, on the integration sign ? To be more precise, consider a function F(x) of one or several variables. Its integral on a...
  20. T

    Low pass filter (arctan domain)

    Homework Statement when I'm trying to calculate and show the graphic of the phase characteristic i don't understand why the domain range of the arctan function is [0,90] : Homework Equations The Attempt at a Solution shouldn't be the domain of arctan function between...
  21. A

    MHB Domain of Square Root Function

    Find the domain of the function f(x)= (3x+5)1/2. Not quite sure how to even start this...
  22. D

    Domain of a Function: Real vs Complex Numbers

    Homework Statement Consider some simple single-variable function such as f(x)=2x+1 The domain,codomain and range of the above function is set of all real numbers. But why not the set of all complex numbers? if x = 3+4i f(x) = 6+8i + 1 = 7+8i,so it is possible for x to be a complex no...
  23. T

    Magnitude in frequency domain of Fourier Transform

    Homework Statement Hi All, I'm just trying to practice graphing signals in frequency domain and I came across a stiuation I wasn't familiar with. If the exp() has a constant*t in it I'm not sure how to graph it, I remember that just cos it like a double sided exp(jwt) but with half the...
  24. nukeman

    Determine the domain and range of the function y=5−e^(−x/2).

    Homework Statement Determine the domain and range of the function y=5−e^(−x/2). I am having some trouble with this. Does any have some tips to get started, or a good link to a instructional video? My textbook does not have this section :( Thanks all! Homework Equations The...
  25. T

    Magnitude in frequency domain of Fourier Transform situation

    Hi All, I'm just trying to practice graphing signals in frequency domain and I came across a stiuation I wasn't familiar with. If the exp() has a constant*t in it I'm not sure how to graph it, I remember that just cos it like a double sided exp(jwt) but with half the magnitude. I've attached a...
  26. J

    Domain of f(x,y) = x^y: All Real Pairs Except (0,0)

    Homework Statement What is the domain of f(x,y)=x^y The Attempt at a Solution I thought it would be all real pairs except (0,0) but it is x>0 and y all real numbers?
  27. B

    Domain, Range & Inverse of a Function

    Homework Statement How to solve part (iv) & (v)Homework Equations general form : y = a(x-h)^2 + kThe Attempt at a Solution In part (iv) for finding domain and range I converted g(x) in general form and then compared it with general form.
  28. E

    On the domain of the function that undergoes the Hilbert transform

    Hi all, This question is on the Hilbert transform, particularly on the domain of the input and output functions of the Hilbert transform. Before rising the question, consider the Fourier transform. The input is f(t) and the output is F(\omega). The function f and F are defined over...
  29. E

    Domain and Range of a function

    Homework Statement If the maximum allowable width, w, of the wall is 100 cm, what are the domain and rand of the function? Remember to include units for both the domain and range. Homework Equations w(d)=2d w(d)=100, so 100=2d, there fore d=100/2 The Attempt at a Solution...
  30. Calculuser

    Domain and Range of A Function

    I have a question about domain and range.What are the domain and range of cos(e^{-×}) and \frac{\left|2×-1\right|}{sin(\frac{1}{2}\pi×-\pi)} ?? Thanks..
  31. binbagsss

    Function Definition / Concept - Codomain, range, domain etc.

    What must actually be specified in order for a function to be fully defined / or in what combinations if not all 3 need to be specified? I.e - from knowing the function you can determine the co-domain - e.g - if it is specified that real functions are going in, and for something simple like 2x...
  32. D

    Characteristic - must be on an integral domain? Books disagree?

    I am reviewing for the mathematics GRE subject exam, and I have this review book, and in the book when they speak of the characteristic of a ring they give the following def "Let R be a ring. The smallest positive integer n such that na = 0 for every a in R is called the characteristic of the...
  33. A

    The correct domain of self-adjointness for the Laplacian

    The "correct" domain of self-adjointness for the Laplacian Consider the Hilbert space L^2(\mathbb R^d), and consider the Laplacian operator \Delta on this space. We want to find a domain, D(\Delta) \subset L^2(\mathbb R^d), such that this guy is a self-adjoint operator. We have been talking...
  34. D

    MHB How to start Laplace infinite domain

    This problem seems a little overwhelming at the point. I am not sure on where and how to start. Suppose that a uniform thermal gradient in the +x direction exists in a very large (i.e. effectively infinite) domain of conductivity $k_2$ such that the temperature field $u_{\infty}(r,\theta)$ can...
  35. L

    Declaring the domain of a function of two variables.

    Homework Statement I have this function of two variables: f(x,y)=\sqrt{4xy-3y^2} Where I have to declare the domain of the function. Homework Equations Since you cannot take the square root of something negative, when dealing with real numbers. The square root has to be zero or...
  36. P

    Differentiation of a function in a domain

    Homework Statement Find the derivatives at an arbitrary point x in the domain of the following functions f_i: D_i → ℝ, where for 1 ≤ i ≤ 6 the domain D_i is the maximal subset of ℝ on which the mapping is defined - you don't have to determine the domains. Homework Equations a) f_1 (a) =...
  37. 1

    What is the domain of sin(arcsin(x))?

    Homework Statement I need to find the domain of sin(arcsin(x)). Now I "know" that this is xε(-1,1), but I don't understand why. If the range of arcsin(x) is (-∏/2,∏/2), then shouldn't this be the domain of sin(arcsin(x))? Help appreciated.
  38. nukeman

    Quick domain of function question: Why do you have 2 cases for this function?

    Homework Statement This question here. Can someone please tell me why we have 2 cases to consider. http://archives.math.utk.edu/visual.calculus/0/domain.1/8.html I don't understand why it says we have 2 cases to consider. 8 x - 4 > 0 and x - 3 > 0. 8 x - 4 < 0 and x - 3 < 0...
  39. X

    Understanding the Image output in Frequency Domain

    I need help understanding how frequencies are distributed when taking the FFT of an Image and how can i determine those frequencies, I really need a detailed and easy tutorial with practical example to understand it. When we take the FFT of a Sine/Cos wave we can easily see its frequencies in...
  40. S

    Find the domain and rainge of this function (rational fn)

    Homework Statement Find domain and range of f(x,y)=\frac{-3y}{x^{2}+y^{2}+1} Homework Equations The Attempt at a Solution It's quite obvious the the domain is R^{2}, because there are no possible values of x or y that would make the denominator 0. But as for the range, my...
  41. S

    What is the generic term for domain & range?

    As I understand it, there are the terms: domain - variables that are input to a function range - the variable that is output to a function This works well in a canonical single equation system like z = f( x , y ), but breaks down in an implicit function or set of equations. I was...
  42. Y

    MHB What is the domain of f(x)=ln(sin(pi/x))?

    Hello guys, I need some assistance in calculating the domain of this function: f(x)=ln(sin(pi/x)) I started with sin(pi/x)>0 due to the ln function. From here 0<(pi/x)<pi. That lead me to some calculations giving x>1, but obviously I have periods of 2*pi to include. The answer is: x>1...
  43. FOIWATER

    Domain of a function - f(x,y)=root(1-x)+root(1-y)

    I have came up with a solution for this - in order for this function to be defined, we must have an x and y between negative infinity up to and including the number 1. If asked to graph this domain, does the domain lie on the x-y plane of three dimensional space, and is it the intersection of...
  44. B

    Finding the domain and range without a calculator

    Homework Statement Find the domain and range of the following function without the use of a calculator: f(x) = sec (pi x/4) Homework Equations As far as I know, this problem doesn't specifically require "equations". Therefore I am leaving this section blank. Not because I am a...
  45. nukeman

    Finding the domain of a composite function help.

    Homework Statement Ok, I just worked out a composite function, and it left me with: √2x^2+5) Now, how do I find the domain from that? I don't understand that my text says the domain of that is just all Real numbers ? What makes this different than other square functions that we are...
  46. nukeman

    Why cant I do this? (Regarding finding domain of function)

    Homework Statement Problem: http://archives.math.utk.edu/visual.calculus/0/domain.1/f6.gif Homework Equations The Attempt at a Solution Look at the pic, and tell me again why I can't do this: http://i47.tinypic.com/bhadsj.jpg
  47. mesa

    Help with domain question with g(f(x))

    Homework Statement If f(x)=√x and g(x)=√(x^2+1) what is the domain of g(f(x))? The Attempt at a Solution I cam up with (-∞,+∞) since the square root of a square is always positive, am I missing something here?
  48. R

    Unique factorization domain, roots of a polynomial, abstract algebra

    Homework Statement let A be a UFD and K its field of fractions. and f\in A[x] where f(x)=x^{n}+a_{n-1}x^{n-1}+...+a_{1}x+a_{0} is a monic polynomial. Prove that if f has a root \alpha=\frac{c}{d}\in K,K=Frac(A) then in fact \alpha\in A I need some guidance with the proof. Proof...
  49. nukeman

    Finding the domain of a function (Sqr root)

    Homework Statement Here is a picture of the question: Homework Equations The Attempt at a Solution Here it what I did... factored it...so 1 / (x-3)(x+17) domain: (-infinity, -3)(-3,17)(17, +infinity) or rather (-3,17) I know that is not correct. I am really stuck on this one!
  50. M

    What is the domain of f(x)=x^(2/3)?

    What is the domain of f(x)=x^(2/3)? If I take a negative number and square it, the result is positive. For example, (-4)^2 is 16. The cube root is 16 is also a positive number. So I conclude that the domain of this function is "all real numbers". But in Wolfram the answer is "all...
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