What is Continuous: Definition and 1000 Discussions

In mathematics, a continuous function is a function that does not have any abrupt changes in value, known as discontinuities. More precisely, a function is continuous if arbitrarily small changes in its output can be assured by restricting to sufficiently small changes in its input. If not continuous, a function is said to be discontinuous. Up until the 19th century, mathematicians largely relied on intuitive notions of continuity, during which attempts such as the epsilon–delta definition were made to formalize it.
Continuity of functions is one of the core concepts of topology, which is treated in full generality below. The introductory portion of this article focuses on the special case where the inputs and outputs of functions are real numbers. A stronger form of continuity is uniform continuity. In addition, this article discusses the definition for the more general case of functions between two metric spaces. In order theory, especially in domain theory, one considers a notion of continuity known as Scott continuity. Other forms of continuity do exist but they are not discussed in this article.
As an example, the function H(t) denoting the height of a growing flower at time t would be considered continuous. In contrast, the function M(t) denoting the amount of money in a bank account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.

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  1. S

    A Can quantum cellular automata simulate quantum continuous processes?

    Can quantum cellular automata/quantum game of life simulate quantum continuous processes in the continuous limit? At the end of this article: https://hal.archives-ouvertes.fr/hal-00542373/document it is said that: "For example, several works simulate quantum field theoretical equations in the...
  2. T

    Showing that an exponentiation is continuous -- Help please....

    Homework Statement Let ##p\in\Bbb{R}##. Then the function ##f:(0,\infty)\rightarrow \Bbb{R}## defined by ##f(x):=x^p##. Then ##f## is continuous. I need someone to check what I've done so far and I really need help finishing the last part. I am clueless as to how to show continuity for...
  3. A

    A Rigorous transition from discrete to continuous basis

    Hi all, I'm trying to find a mathematical way of showing that given a complete set $$\left |a_i\right \rangle_{i=1}^{i=dim(H)}∈H$$ together with the usual property of $$\left |\psi\right \rangle = ∑_i \left \langle a_i\right|\left |\psi\right \rangle\left |a_i\right \rangle ∀ \left...
  4. Levi Franco

    B Basic Question about absolutely continuous functions

    My question is maybe elementary but I don't know the answer. I have a function f absolutely continuous in (a,c) and in (c,b), f continuous in c. Is f absolutely continuous in (a,b)? I think the answer is negative but I can't find a counterexample. I really apreciatte your help.
  5. V

    B Is space is continuous or discrete?

    I was watching a video where well known physicist Lisa Randall said that we still don't know whether space is continuous or discrete. My question is, how do we find whether space is continuous or discrete?? What type of experiments are possible? Is it being done now?? I am thinking this may be...
  6. I

    Discretize this continuous time linear system

    Homework Statement I need to find the discrete time equivalent of the following system: \begin{bmatrix} \ddot{x} \\ \dot{x} \\ \ddot{\theta} \\ \dot{\theta} \end{bmatrix} = \begin{bmatrix} 0 & 0 & 0 & 4.2042857 \\ 1 & 0 & 0 & 0 \\ 0 & 0 & 0 & 105.1071428 \\ 0 & 0 & 1 & 0 \end{bmatrix}...
  7. J

    Is this function continuous and differentiable?

    Homework Statement Homework Equations Solve using limits. Function is continuous if it's graph is continuous throughout. here the (x-1) term gets canceled in numerator and denominator. So we have a continuous graph of (x+1). The Attempt at a Solution The (x-1) term gets canceled from...
  8. Dor

    I What should be continuous at the interface of two materials?

    At the interface between: 1) conductor/conductor 2) conductor/semiconductor (or dielectric) 3) semiconductor/semiconductor (or dielectric/dielectric) What quantity should be continuous? Is it the electrochemical potential, only the chemical potential or is it the electric potential? Since they...
  9. Mr Davis 97

    Show that this piecewise function is continuous at 0

    Homework Statement ##f(x) = x \sin (\frac{1}{x})## for ##x \ne 0## and ##f(0) = 0##. Prove that this function is continuous at 0. Homework EquationsThe Attempt at a Solution First, I need to look at the quantity ##|f(x) - f(0)|##. However, I am not completely sure how to proceed. I would think...
  10. M

    Rule de l'Hôpital - Continuous and Differentiable

    Homework Statement Prove that ##h: [0,\infty) \rightarrow \mathbb R, x \mapsto \begin{cases} x^x, \ \ x>0\\ 1, \ \ x = 0\\ \end{cases} ## is continuous but not differentiable at x = 0. The Attempt at a Solution To show continuity, the limit as x approaches 0 from the right must equal to 1...
  11. R

    Assume that f is a continuous, real-valued function

    Assume that f is a continuous, real-valued function defined on a metric space X. If {xn} is a sequence in X converging to x, prove that Limn→∞f(xn) = f(x). Here is my attempt, but I am not sure if it is correct.
  12. P

    MHB How can i set this problem as a continuous markov chain?

    I request your help in order to know, how can i configure this problem as a continuous markov chain, need to define the main variable, the states, transition rates, and the matrix. I thought that it could be relationed with the independent status of the machines, because if the machine 1 is...
  13. M

    MHB Gamma function is convergent and continuous

    Hey! :o I want to show that the Gamma function converges and is continuous for $x>0$. I have done the following: The Gamma function is the integral \begin{equation*}\Gamma (x)=\int_0^{\infty}t^{x-1}e^{-t}\, dt\end{equation*} Let $x>0$. It holds that...
  14. Y

    Consequences of time not being continuous

    Homework Statement Given that the phenomena of time is non continuous, despite it often being considered as being so, what are the consequences of this? It seems that the foundation of mathematics that describes the physical world assumes that time is continuous, which we believe now to be...
  15. F

    Convergence of a continuous function related to a monotonic sequence

    Homework Statement Let ##f## be a real-valued function with ##\operatorname{dom}(f) \subset \mathbb{R}##. Prove ##f## is continuous at ##x_0## if and only if, for every monotonic sequence ##(x_n)## in ##\operatorname{dom}(f)## converging to ##x_0##, we have ##\lim f(x_n) = f(x_0)##. Hint: Don't...
  16. S

    Pressure in a tank with continuous flow

    I feel like this is easy to answer but I'm coming up with answers I don't trust. Basically, I have a tank of air where I want to keep the pressure at a certain value. Let's say 1 psig for the sake of argument. I have a 1/2" ID hose connecting to inlet flow to the tank and an outlet hose of 3/4"...
  17. qttv

    A Classical Mechanics: Continuous or Discrete universe

    Good morning. The question of the "continuous" or "discrete" nature of the universe is the subject of diatribe among the greatest physicists in the world. I would like to discuss the same topic, but asking a question about the aspect of continuum in classical mechanics. The use of mathematical...
  18. O

    Step potential, continuous wave function proof

    Homework Statement I am being asked to show that the wave function ψ and dψ/dx are continuous at every point of discontinuity for a step potential. I am asked to make use of the Heaviside step function in my proof, and to prove this explicitly and in detail. Homework Equations...
  19. B

    I Continuous Lensing Models: Discrete Data

    Hello, I am not sure if this question is better suited to the mathematics section, but I thought it would be easier to explain the problem here. In Schneider, Kochanek and Wambsganss's "Gravitational Lensing: Strong Weak and Micro" pages 279-280, they derive a relation for determining the...
  20. Math Amateur

    MHB Linear Mappings are Lipschitz Continuous .... D&K Example 1.8.14 .... ....

    I am reading "Multidimensional Real Analysis I: Differentiation" by J. J. Duistermaat and J. A. C. Kolk ... I am focused on Chapter 1: Continuity ... ... I need help with an aspect of Example 1.8.14 ... ... The start of Duistermaat and Kolk's Example 1.8.14 reads as...
  21. Math Amateur

    MHB The Euclidean Norm is Lipschitz Continuous .... D&K Example 1.3.5 .... ....

    I am reading "Multidimensional Real Analysis I: Differentiation" by J. J. Duistermaat and J. A. C. Kolk ... I am focused on Chapter 1: Continuity ... ... I need help with an aspect of Example 1.3.5 ... ... The start of Duistermaat and Kolk's Example 1.3.5 reads as...
  22. G

    I Disctrete vs continuous spectrum

    I’ve been digging around trying to get at the physical basis for the black body spectrum. Say I have a neutral gas,non ionized. This has its own discrete spectrum. Are the mechanisms of line broadening the reason why we seek continuous spectrum in the back body curve? That’s question 1. No 2...
  23. Math Amateur

    MHB A Further Question on Proper and Continuous Mappings .... D&K Theorem 1.8.6 ....

    I am reading "Multidimensional Real Analysis I: Differentiation" by J. J. Duistermaat and J. A. C. Kolk ... I am focused on Chapter 1: Continuity ... ... I need help with another aspect of the proof of Theorem 1.8.6 ... ... Duistermaat and Kolk"s Theorem 1.8.6 and the preceding definition...
  24. Math Amateur

    MHB Proper and Continuous Mappings in R^n .... ....

    I am reading "Multidimensional Real Analysis I: Differentiation" by J. J. Duistermaat and J. A. C. Kolk ... I am focused on Chapter 1: Continuity ... ... I need help with an aspect of the proof of Theorem 1.8.6 ... ... Duistermaat and Kolk"s Theorem 1.8.6 and the preceding definition...
  25. Math Amateur

    MHB Continuous Functions and Open Sets .... D&K Example 1.3.8 ....

    I am reading "Multidimensional Real Analysis I: Differentiation" by J. J. Duistermaat and J. A. C. Kolk ... I am focused on Chapter 1: Continuity ... ... I need help with an aspect of Example 1.3.8 ... Duistermaat and Kolk"s Example 1.3.8 reads as follows:In the above example we read the...
  26. J

    Principle of virtual work for continuous systems

    I always thought that the principle of virtual work (PVW) is valid for all structures, including continuous structures (like bars, beams, plates, etc.). However, in his book 'Fundamentals of Structural Mechanics', Hjelmstad states that the PVW is only valid for discrete systems with N particles...
  27. M

    MHB Find a function so that the composition is continuous

    Hey! :o For which real constants $a,b,c$ is the following function $f$ continuous on $\mathbb{R}$ ? $$f(x)=\begin{cases}1+x^2 & \text{ for } x\leq 1, \\ ax-x^3 & \text{ for } 1<x< 2 \\ b & \text{ for } x=2\\ cx^2 & \text{ for } x>2\end{cases}$$ For $a=1, b=-6, c=-\frac{3}{2}$ the function...
  28. I

    Continuous Grey Atmosphere Model

    Homework Statement In the grey atmosphere radiative energy balance model, we replace the multi-layer approximation used above with still simplified but significantly more realistic model involving a continuous atmosphere with a continuously varying temperature. The variation with temperature is...
  29. T

    Why is blackbody radiation continuous?

    Plasmas can emit radiation based on the acceleration of charged particles (which we generally consider as continuous), but for un-ionized matter compounds, transitions are quantized and photons have particular energies. At room temperature, collisional excitations are typically dominant. But if...
  30. Dopplershift

    I Understanding Continuous Variable QKD

    So, I am doing my undergraduate research project in Quantum Cryptography, and I have some confusion in a few areas, especially in the topic of continuous variable quantum key distribution. From what I understand, Discrete Variable - Single photon. That is, for example, the BB84 protocol. Bob...
  31. B

    Gravitational potential energy and continuous matter

    The gravitational potential energy of two massic points ##P_1## and ##P_2## with respective masses ##m_1## and ##m_2## is given by $$U = -G \frac{m_1 m_2}{|| P_2 - P_1 ||}$$ Now I was wondering how this formula could be applied to continuous matter. Let us imagine a very simple case where we...
  32. I

    B Inner product of functions of continuous variable

    I am new to quantum mechanics and I have recently been reading Shankar's book. It was all good until I reached the idea of representing functions of continouis variable as kets for example |f(x)>. The book just scraped off the definition of inner product in the discrete space case and refined it...
  33. G

    Intersecting 2 continuous laser in thin air to create a dot

    I am planning on making an experiment about intersecting continuous wave laser from 2 or more source on 1 point in thin air. The laser i am planning to use is the simple laser diode, pumped with continuous wave, instead of using pulsed wave as in the usual laser pointer as i don't need it to...
  34. B

    Composition of a Continuous and Measurable Function

    Homework Statement Suppose that ##f## and ##g## are real-valued functions defined on all of ##\Bbb{R}##,##f## is measurable, and ##g## is continuous. Is the composition ##f \circ g## necessarily measurable? Homework EquationsThe Attempt at a Solution Let ##c \in \Bbb{R}## be arbitrary. Then...
  35. dextercioby

    I Continuity of the determinant function

    This is something I seek a proof of. Theorem: Let ## \mbox{det}:\mbox{Mat}_{n\times n}(\mathbb{R}) \rightarrow \mathbb{R}## be the determinant function assigned to a general nxn matrix with real entries. Prove this mapping is continuous. My attempt. Continuity must be judged in...
  36. T

    Continuous slab / freely supported slab

    Homework Statement I was told that for continuous slab , it can be only for 2 ways slab. While for freely supported slab , it can be either 2 ways or 1 way slab. P/s : for one way slab , the Ly/Lx <2 . For 2 ways slab , Ly/Lx > 2 . Homework EquationsThe Attempt at a Solution I think it's...
  37. PsychonautQQ

    I Noncompact locally compact Hausdorff continuous mapping

    Self studying here :D... Let X and Y be noncompact, locally compact hausdorff spaces and let f: X--->Y be a map between them; show that this map extends to a continuous map f* : X* ---> Y* iff f is proper, where X* and Y* are the one point compactifications of X and Y. (A continuous map is...
  38. Math Amateur

    MHB Continuous Functions on Intervals .... B&S Theorem 5.3.2 ....

    I am reading "Introduction to Real Analysis" (Fourth Edition) by Robert G Bartle and Donald R Sherbert ... I am focused on Chapter 5: Continuous Functions ... I need help in fully understanding an aspect of the proof of Theorem 5.3.2 ...Theorem 5.3.2 and its proof ... ... reads as follows:In...
  39. PsychonautQQ

    Open/Closed continuous maps between the plane

    Homework Statement Give examples of maps between subsets of the plane (with Euclidean toplogy) that are: a) open but not closed or continuous b) closed but not open or continuous c) continuous and open but not closed e) continuous and closed but not open f) open and closed but not continuous...
  40. P

    MHB James' question about a continuous probability distribution

    Since it's a PDF, that means the entire area under the curve must be 1, so $\displaystyle \begin{align*} \int_0^1{ a \left( x^2 + b \right) \,\mathrm{d}x } &= 1 \\ a \left[ \frac{x^3}{3} + b\,x \right] _0^1 &= 1 \\ a \left[ \left( \frac{1^3}{3} + b\cdot 1 \right) - \left( \frac{0^3}{3} + b...
  41. Math Amateur

    MHB Continuous Functions - Thomae's Function ....

    I am reading "Introduction to Real Analysis" (Fourth Edition) b Robert G Bartle and Donald R Sherbert ... I am focused on Chapter 5: Continuous Functions ... I need help in fully understanding an aspect of Example 5.1.6 (h) ...Example 5.1.6 (h) ... ... reads as follows: In the above text from...
  42. B

    Extending a Continuous Function a Closed Set

    Homework Statement Let ##E## be a closed set of real numbers and ##f## a real-valued function that is defined and continuous on ##E##. Show that there exists a function ##g## defined and continuous on all of ##\Bbb{R}## such that ##f(x) = g(x)## for each ##x \in E##. Homework EquationsThe...
  43. L

    MHB Proving Continuous Extension of $f(x,y)$ Function

    Can I extend the function $f(x,y)=(x^2+y^2)\arctan\dfrac{1}{|xy|}$ to a continuous function? If I consider the restriction of $f$ along the line $x=k$ i find $\lim_{(x,y)\rightarrow(k,0)}(x^2+y^2)\arctan\dfrac{1}{|xy|}=k^2\dfrac{\pi}{2}$ how can i prove that?
  44. D

    Water level rise in a tank, continuous flow in, high exit

    Homework Statement : See below paragraphs[/B] Homework Equations : I'm not sure on which equations I need.[/B] The Attempt at a Solution : I'm so sorry, this really isn't my strong point. Using the figures below, the tank surface is 113.184 sq in. The side pipe has a cross section area of 3.14...
  45. jaketodd

    I Question about modeling continuous spacetime

    Since determining how many points there are in a given volume of continuous spacetime would require divisibility by infinity, is set theory's infinite sets the only way to model continuous spacetime? Thanks, Jake
  46. I

    Light bulbs -- is there a continuous wave spreading out?

    When a light bulb is emitinting light, is there a continuous wave spreading out, or is there a large number of particles (photons) emitted in random directions, which in the conglomerate, mimics a single continuous wave spreading out.
  47. T

    Can electric motors possibly apply continuous upward force?

    Is it possible for an electric motor to exist (based on our current understanding) which is capable of applying continuous upward force upon an object, enabling that object to fly or lift above the air?
  48. P

    Prove that the logarithmic function is continuous on R.

    Homework Statement Prove that f\left(x\right)=\log_{a}x is continuous for all \mathbb{R}. Homework Equations [/B] I must find a \delta>0\in\mathbb{R} for a given \varepsilon>0 such that \left|x-x_{0}\right|<\delta\Rightarrow\left|\log_{a}x-\log_{a}x_{0}\right|<\varepsilon. The Attempt at a...
  49. A

    I General question about how objects move nature (discrete or continuous?)

    Hello everyone! I hope I write in right forum branch. The reason is that I have a question in my mind for a while. Maybe you can help to understand it. So, I am game developer, and one time I was using 2d physics engine to simulate motion in game. And I found out that in that engine, for...
  50. L

    A IS THERE A FENCEPOST ERROR WHEN CALCULATING MASS FOR A CONTINUOUS DISTRIBUTION?

    Let's say 5 masses are arranged on x axis. At x=1, 2kg X=2, 4kg X=3, 6kg X=4, 8kg X=5, 10 kg Obviously, there is a total mass of 30 kgIf the mass is distributed continuously by the function M(x) = 2x, then From x= 0 to x=5, there is 25 kg of mass from the simple integral. WHY IS THERE LESS...
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