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account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.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. H

    I Why must the wave function be continuous in an infinite well?

    It is required to be continuous in the following text: The book's reason why wave functions are continuous (for finite V) is as follows. But for infinite V, ##\frac{\partial P}{\partial t}=\infty-\infty=## undefined, and so the reason that wave functions must be continuous is invalid...
  2. H

    I Why probability current = 0 at infinity? Why must wavefunction be continuous?

    Q1. Why is the probability current ##j(x,t)=0## at ##x=\pm\infty##? (See first line of last paragraph below.) My attempt at explaining is as follows: For square-integrable functions, at ##x=\pm\infty##, ##\psi=0## and hence ##\psi^*=0##, while ##\frac{\partial\psi}{\partial x}## and hence...
  3. V

    A Game Theory: Are the payoff functions πi continuous?

    How do I show that the payoff function πi isn´t continuous? Why do best replies not always exist?
  4. Mr Davis 97

    I Continuity of composition of continuous functions

    I've learned that composition of continuous functions is continuous. ##\log x## and ##|x|## are continuous functions, but it seems that ##\log |x|## is not continuous. Is this the case?
  5. B

    Electric field by continuous charge distributions.

    While reading the book, Electricity and magnetism, the author says that electric field just outside a spherical shell is ##4\pi \sigma##, on it ##4\pi\sigma r_0^2## ,inside is ##0## and outside is ##Q/R^2##. My derivations :- For inside, ##E\Delta S = 4\pi Q = 0## since ##Q = 0##. For...
  6. I

    Show that the map is continuous

    Homework Statement Consider the map F: R^3 →R^2 given by F(x,y,z)= ( 0.5⋅(e^(x)+x) , 0.5⋅(e^(x)-x) ) is continuous. Homework EquationsThe Attempt at a Solution [/B] I want to use the definition of continuity which involves the preimage: ""A function f defined on a metric space A and with...
  7. FallenApple

    A Different results for factor vs continuous

    So, I'm doing an interaction model with response vs treatment_type interaction with age+controls(for confounders) with age being continous, say patients ranging from 20 years old to 90 years old. so I have two models. y=age+treatment_type . + . age*treatment_type y=factor(age)+treatment_type...
  8. Biker

    B Continuous random variable: Zero probablity

    I just have a couple of questions about how it can be zero probability. In case, you have a continuous cumulative probability distribution such that there is a derivative at each point not equal to zero. This means that every point as a different value than the other which means that every...
  9. A

    Proving Completeness of Continuous Basis Vectors

    Homework Statement Consider the vector space that consists of all possible linear combinations of the following functions: $$1, sin (x), cos (x), (sin (x))^{2}, (cos x)^{2}, sin (2x), cos (2x)$$ What is the dimension of this space? Exhibit a possible set of basis vectors, and demonstrate that...
  10. Archie Medes

    Transform difference equation into continuous function?

    Homework Statement My question: Can I turn this difference equation for R below, into a continuous function R(t)? I have no idea if, or how, I can. And I'd like to. Equation derived from the following manufacturer statement on the thermal response of a thermistor to a fixed temperature: The...
  11. Eclair_de_XII

    Courses Taking continuous probability over discrete probability?

    I'm considering taking the upper-level probability course at my school over the elementary course offered because of time constraints. The latter is not a prerequisite for the former. Do you think I will be alright taking the more advanced probability course over the elementary course? Any input...
  12. BrainMan

    Continuous Distribution of Charges Problem

    Homework Statement Charge Q is uniformly distributed along a thin, flexible rod of length L. The rod is then bent into the semicircle shown in the figure (Figure 1) . Find an expression for the electric field E⃗ at the center of the semicircle. Hint: A small piece of arc length Δs spans a...
  13. B

    Coarsest Topology With Respect to which Functions are Continuous

    Homework Statement See attached picture.Homework EquationsThe Attempt at a Solution At the moment, I am dealing with part (a). What I am perplexed by is the ordering of the parts. If the subbasis in part (b) does indeed generate this coarsest topology, why wouldn't showing this be included in...
  14. T

    Continuous uniform distribution function

    Homework Statement Can someone explain why f(x) = 1/(b-a) for a<x<b ? Homework EquationsThe Attempt at a Solution shouldn't it be 0? since its a continuous random variable and so that interval from a to b has an infinite number of possible values?
  15. FritoTaco

    Find the values of a and b that make f continuous everywhere

    Homework Statement Find the values of a and b that make f continuous everywhere. See attachment for the function. I'm suppose to find a and b. Homework Equations The Attempt at a Solution See the second attachment The problem I have is, when I get to the last step, I'm trying to cancel...
  16. M

    MHB F is continuous if and only if f is continuous at 0

    Hey! :o Let $f : \mathbb{R}\rightarrow \mathbb{R}$ be a function with $ f(x + y) = f(x) + f(y)$ for all $x, y \in \mathbb{R}$. I want to show that $f$ is continuous if and only if $f$ is continuous at $0$. I have done the following: $\Rightarrow$ : This direction is trivial. $f$ is...
  17. R

    Continuous random variable transformation and marginals

    On the attachment, I was told my joint pdf was right, but the support was NOT 0<y1y2<1 0<y2<1, so maybe it's right now? Obviously B and C are incorrect, too, since they don't integrate to 1. I'm probably making just a few simple mistakes. Thanks in advance!
  18. A

    Potential difference due to a continuous charge distribution

    This is my first time using this site so please excuse me if I missed any guidelines. 1. Homework Statement A plastic rod having a uniformly distributed charge Q=-25.6pC has been bent into a circular arc of radius R=3.71cm and central angle ∅=120°. With V=0 at infinity, what is the electric...
  19. I

    B Is distance continuous or "pixel" like?

    Essentially I'm asking if space is divided into stepping stones, pixels if you will. Whereby the absolute minimum distance you can travel is this distance? Another way of asking about this is, if you took a finite area of space, are there infinite positions within this space?
  20. T

    MHB Continuous Compounding over 12 months (finding the rate)

    This problem is actually for a program I'm writing and I've forgotten my basic maths.I have an initial value starting at period 0 . That value is 20. At the end of 12 periods (period 12) I have a value of 33. So I know the last value is 33 and the first value is 20 and I want to find the...
  21. G

    I Discrete vs Continuous Spectra in Blackbody Radiation?

    I was reading this article which talks about the theoretical model behind blackbody spectra: http://www.cv.nrao.edu/course/astr534/BlackBodyRad.html At the start, it mentions standing waves in a cavity. Standing waves in this model consist of an integer number of wavelengths. The standing waves...
  22. Domenico94

    Continuous and discrete spectra

    Is there any way to convert a continuous, aperiodic spectrum, to a discrete spectrum, in a signal? If so, would part of he energy of this signal be lost, I am this process of conversion, or would it be " distributed" amomg the various frequencies?
  23. mertcan

    I P(X=x) in continuous distributions

    hi,initially I am aware that for continuous distributions, P(X=x) always equals zero, but when I look at some derivations as the attachment I see that for exponential variable they use exponential pdf when they want to find P(X1=x). My question is : if we say that for continuous distributions...
  24. Peeter

    Magnetostatics force equation for continuous current density

    In Jackson, the following equations for the vector potential, magnetostatic force and torque are derived##\mathbf{m} = \frac{1}{{2}} \int \mathbf{x}' \times \mathbf{J}(\mathbf{x}') d^3 x'## ##\mathbf{A} = \frac{\mu_0}{4\pi} \frac{\mathbf{m} \times \mathbf{x}}{\left\lvert {\mathbf{x}}...
  25. A

    Finding value of c that makes function continuous

    Homework Statement f(x)= (sincx/x) ; x<0 1+(c)(tan2x/x) ; x≥0 Homework EquationsThe Attempt at a Solution Lim as x tends to 0+[/B] = 1+c⋅2⋅(sin2x/2x)⋅(1/cos2x) =1+c⋅2⋅1⋅1= 1+2c Lim as x tends to 0 - = (sincx/x)=(c/1)⋅(sinx/x)=c⋅1=c Equating both: 1+2c=c...
  26. U

    MHB Is only (i) true for a continuous function f with given conditions?

    Hi there, I'm having trouble with the above question. Basically, I need to determine which, or all of the statements are true. I've tried coming up with different ways the function can look like to satisfy or not satisfy the statements, but have come to no luck in doing so. If anyone could...
  27. T

    MHB Finding Continuous Values of $\frac{e^{sinx}}{4 - \sqrt{x^2 - 9}}$

    I have this function $$\frac{e^{sinx}}{4 - \sqrt{x^2 - 9}}$$ And I need to find all the values for which this function is continuous. So I do $$4 - \sqrt{x^2 - 9} \ne 0$$ $$ \sqrt{x^2 - 9} \ne 4 $$ $$ x^2 - 9 \ne 16 $$ $$ x^2 \ne 7 $$ And therefore, the function is not valid where...
  28. M

    Linear transformations, images for continuous functions

    Homework Statement Let ##C## be the space of continuous real functions on ##[0,\pi]##. With any function ##f\in C##, associate another function ##g=T(f)## defined by $$g=T(f)\equiv \int_0^\pi \cos(t-\tau) f(\tau) \, d \tau$$ a) Show ##T## is a linear transformation from ##C## to ##C##. b)What...
  29. U

    MHB Finding the value of the constant that makes the function continuous?

    Hello, I am finding this questions quite difficult, can someone please offer some insight as to what needs to be done. Do we need to do limit tests to the left and right of x = 7?
  30. S

    How to make functions right-continuous

    Homework Statement Given r(t)=\left< \frac { sint }{ t } ,\frac { { e }^{ 2t }-1 }{ t } ,{ t }^{ 2 }ln(t) \right> Re-define r(t) to make it right continuous at t=0 Homework EquationsThe Attempt at a Solution This is probably the simplest problem ever, but I don't even know what it's asking...
  31. G

    B Continuous Function: Exploring Definition & Difference

    What do we mean when we say a function is continuous on its domain? How is that different from simply saying that a function is continuous?
  32. A

    A Problem in continuous function of Excimer laser

    I am student of MS and working in the field of laser. I am trying to run an old Excimer laser system (XeCl) having output energy 400mJ, pulse width 30ns and frequency 1-100Hz. The laser works only for less than one hours after filling with new gases and the energy continuously decreases within...
  33. FeDeX_LaTeX

    I Discrete Convolution of Continuous Fourier Coefficients

    Suppose that we have a 2\pi-periodic, integrable function f: \mathbb{R} \rightarrow \mathbb{R}, whose continuous Fourier coefficients \hat{f} are known. The convolution theorem tells us that: $$\displaystyle \widehat{{f^2}} = \widehat{f \cdot f} = \hat{f} \ast \hat{f},$$ where \ast denotes the...
  34. M

    A Does continuous mass distribution implies finite propagation

    speed? This question emerged in my mind while studying a discrete and continuous mathematical model of a falling slinky. In the discrete model, we suppose an instantaneous interaction between mass points at a distance, so the action propagates through the chain of mass points with infinite...
  35. B

    I A Question about Notation and Continuous Linear Functionals

    I have reading through various sources on linear functionals, but all seem somewhat inconsistent with regard to denoting the set of all linear functionals and the set Also, what is the standard definition of a continuous linear functional? I really couldn't find much besides this Let ##f : V...
  36. orion

    I Boundedness and continuous functions

    I am working my way through elementary topology, and I have thought up a theorem that I am having trouble proving so any help would be greatly appreciated. ---------------------- Theorem: Let A ⊂ ℝn and B ⊂ ℝm and let f: A → B be continuous and surjective. If A is bounded then B is bounded...
  37. A

    Force at a point by continuous charge distribution....

    Homework Statement This is more of a general question, but a simple example would be find the force on a test charge q at the center of a ring of charge with a total charge Q and a charge distribution given as λ(θ) =ksin(θ) where θ is measured clockwise with respect to the positive x-axis. The...
  38. Joseph Richard

    Continuous Ratio Conditions: Product of 1296, Last Term 1/6 of Sum of Means

    Homework Statement Determine the conditions of a continuous ratio knowing that the product of the four terms is 1296 and the last term is equal to 1/6 of the sum of means. Original question (in Portuguese): Determinar as condições de uma proporção contínua sabendo que o produto dos quatro...
  39. Pattonias

    Aspect Ratio of Continuous Cast Rolled Steel

    We have a requirement that if our pipe is going to be fabricated from plate, then it must have a larger than 6-to-1 reduction from the original conventionally cast ingot or continuously cast slab. It is not specified whether this would be hot/cold rolling, but we figured that .5 inch plate...
  40. KF33

    Solving Continuous Functions Homework: Need Help with a and b

    Homework Statement The problem is posted below in the picture. I looked at c and d and can do those. I am unsure about a and b. Homework EquationsThe Attempt at a Solution I looked at graphing the problems, but I think it is a wrong approach.
  41. KF33

    I Continuous Functions with Piecewise Functions

    I have been working on this exercise 5 and kind of stuck how to start the problems. I would think to start with a graph, but I feel this is wrong. I am just stuck on a and b.
  42. K

    MHB Determine if a function is continuous

    f(x)=\begin{cases}\dfrac{x^2-4}{x+2}, & x\ne-2 \\[3pt] 4, & x=-2 \\ \end{cases} Determine if its continuous at x=-2
  43. F

    A Continuous map from one manifold to another

    I need a reminder. What numbers or functions characterize a map from one manifold to another? More specifically, is there a continuous function that goes from one manifold to another to another to another is some parameterized way? What is that called? I'm thinking of a manifold of spacetime...
  44. Z

    I Discrete Random Vectors vs. Continuous Random Vectors

    Given a continuous random vector (X,Y) with a joint density function In order to check whether it is indeed a joint density ƒ(x,y) the method is to check if ∫∫ƒ(x,y)dxdy=1 where the integrals limits follow the bounds of x and y. However, is it the case that if given an arbitrary discrete random...
  45. P

    B Is the Universe discrete or continuous?

    Apologies if this question has been asked already. I've been given resources to help me understand, but it's been hard for me to wrap my head around the answer and, for that matter, it is difficult to understand a text when you have to look up every other word (an exaggeration, but you know ...
  46. E

    Rate of continuous creation

    Question: Estimate the rate of continuous creation required to keep the density of the universe constant at 10-26kg/m3. Express your answer in protons/year/km3. Attempt: Assuming a spherical matter-dominated Friedmann universe, we know from solving the fluid equation that ρ ∝ 1/a3 (where ρ is...
  47. R

    Prove Continuous Functions Homework: T Integral from c to d

    Homework Statement Prove $$T\int_c^d f(x,y)dy = \int_{c}^dTf(x,y)dy$$ where $$T:\mathcal{C}[a,b] \to \mathcal{C}[a,b]$$ is linear and continuous in L^1 norm on the set of continuous functions on [a,b] and $$f:[a,b]\times [c,d]$$ is continuous. Homework EquationsThe Attempt at a Solution [/B]...
  48. S

    Moment in a Continuous beam

    Is the moment in a continuous beam maximum when there is one point load because if you had multiple point loads they would cancel each other out since there are several pin connections along the beam? For example, if I had a 20 kip load moving across a continuous beam and found the maximum...
  49. S

    A Continuous Multivariate Distribution

    Homework Statement The random variable ##(x,y)## has density ##f(x,y) = ce^{-(ax+by)}## for ##0\leq y\leq x\leq 1##, with given constants ##a > 0##, ##b > 0##. 1. Compute the constant ##c##. 2. Find the conditional probability density ##f_y(y|x)##. 3. Compute the regression curve of ##Y## on...
  50. lep11

    Prove functions f and g are continuous in the reals

    Homework Statement Prove functions f and g are continuous in ℝ. It's known that: i) lim g(x)=1, when x approaches 0 ii)g(x-y)=g(x)g(y)+f(x)f(y) iii)f2(x)+g2(x)=1 The Attempt at a Solution [/B] g(0) has to be equal to 1 because it's known that lim g(x)=1, when x approaches 0. Otherwise g won't...
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