Continuous Definition and 1000 Threads

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account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.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

    Cardinality of continuous functions

    Homework Statement What is the cardinality of the set of all continuous real valued functions [0,1] \rightarrow R . The Attempt at a Solution In words: I will be using the Cantor Bernstien theorem. First the above set, let's call it A, is lesser then or equal to the set of all...
  2. K

    Probability - continuous random variables

    Homework Statement Ok, I have 2 questions: 1. Nicotine levels in smokers can be modeled by a normal random variable with mean 315 and variance 1312. What is the probability, if 20 smokers are tested, that at most one has a nicotine level higher than 500? 2. fX,Y (x,y) = xe-x-y...
  3. H

    Solving "Find k if g(x) is Continuous

    Homework Statement g(x)={x+3, x=3 {2+\sqrt{k} , x=3 find k if g(x) is continuous Homework Equations The Attempt at a Solution I have no idea how to begin, but drawing the first part on a cartesian plane.
  4. K

    Show that arctan(x) exists and is continuous

    Homework Statement Show tan(x): (-pi/2, pi/2) -> R has a continuous inverse arctan(x) : R -> (-pi/2, pi/2). You may assume that tan(x) is continuous and strictly increasing on the given domain, and tends to +/- \infty at +/- pi/2 Homework Equations The Attempt at a Solution I...
  5. K

    Continuous random variable - transformation using sin

    Homework Statement There is a pin of length 4 which appear on a photograph, and the length of the image observed is y, an observation on the random variable Y. The pin is at an angle x, 0\leqx\leq\pi/2, to the normal to the film, this is an observation on the r.v. X. 1. If all angles X...
  6. K

    Non 1-1 transformation of continuous random variable

    Homework Statement X is exponentially distributed with mean s. Find P(Sin(X)> 1/2) Homework Equations fX(x) = se-sx, x\geq 0 0, otherwise FX(x) = 1 - e-sx, x\geq 0 0 otherwise The Attempt at a Solution Let Y = sin X FY (y) = P(Y\leq y) = P(sinX \leq Y) = P(X \leq...
  7. K

    Continuous bounded function - analysis

    Homework Statement Assume the theorem that a continuous bounded function on a closed interval is bounded and attains its bounds. Prove that if f: R -> R is continuous and tends to +\infty as x tends to +/- \infty then there exists an x0 in R such that f(x) \geq f(x0) for all x in R...
  8. R

    Can a function be continuous on a composed interval?

    Can a function be continuous on a composed interval? For example, if f(x)=\frac{1}{x} then on the interval (-\infty,0) \cup (0,\infty), f(x) is continous? Or is the function f(x) continuous on (-\infty,0) by itself and (0,\infty) by itself (If you don't get what I'm trying to say reply back)?
  9. K

    Can I solve the discreate ODE by considering the continuous case?

    There is a linear version of so-called lattice Schrodinger equation (LSE), it is just a variation form of nonlinear Schrodinger equation. But the LSE is the discrete case on N lattices. I wonder if I can solve the continuous case and then take the solution at specific lattice for the discrete case?
  10. I

    Qn : Does a continuous function always have a fixed point in [0, 1]?

    I hope someone can help me wif this qnestion. Qn : Let f ; g be continuous functions from [0, 1] onto [0, 1]. Prove that there is x0 ∈ [0, 1] such that f (g(x0)) = g(f (x0)). Thanks in advance.
  11. A

    Piecewise continuous -> NO vertical asymptotes

    Piecewise continuous --> NO vertical asymptotes Why is it impossible for a piecewise continuous function to have vertical asymptotes, per this website: http://www.mathwords.com/p/piecewise_continuous_function.htm?
  12. L

    Electric Field of a Continuous Charge Distribution problem

    The most general way of calculating the value of the vector electric field at a certain point P is given by the formula E = k times Integral of (dq/r² times unit vector). That means you break the charge distribution into infinitesimal elements dq and vectorially add the contributions of each at...
  13. Chewy0087

    Continuity of Multivariable Functions

    EDIT: just realized i might've been really stupid; very simple question which will answer my stupidly long question; is f(x) = 1 continuous?] The reason I ask is that my book says; f(x,y) \in C^{N} in R \Leftrightarrow \frac{\partial ^{n} f}{\partial x^n} , \frac{\partial ^{n} f}{\partial...
  14. N

    Is space continuous or discrete?

    Dear All, I’ve been wondering about the “Is space continuous or discrete?”-debate recently. My question is the following: as far as I know, Heisenberg’s uncertainty principle and quantum mechanics are the main reasons why we believe it is discrete. Are these the only theories which predict...
  15. M

    Continuous square root function on the space of nxn matrices

    Homework Statement Hi again all, I've just managed to prove the existence (non-constructively) of a 'square root function' f on some open epsilon-ball about the identity matrix 'I' such that [f(A)]^2=A\qquad \forall\, A \,\text{ s.t.}\, \|I-A\|<\epsilon within Mn, the space of n*n matrices...
  16. N

    Correlation coefficient between continuous functions

    Hi all, The correlation coefficients (Pearson's) is usually defined in terms of discrete sampling of a function. However, I have seen that the mean and standard deviation, for example, are also typically written in terms of discrete variables BUT may also be expressed in terms of a...
  17. M

    Proving a function is discontinuous on Q and continuous on R\Q

    I have cast my post in LaTeX here: http://www.michaelwesolowski.com/asdjhf.pdf Any and all help is appreciated!
  18. A

    Riemann integrable functions continuous except on a set of measure zero?

    Is it true that a function is Riemann integrable on a bounded interval only if it's equal to a continuous function almost everywhere? I'd imagine this is the case, given the Riemann-Lebesgue lemma, which says that a function is RI iff its set of discontinuities has measure zero. (So the...
  19. L

    [f(x)'^n continuous at a point (EXAM IN 4 hrs.)

    Homework Statement Suppose f: D-->R is continuous at a. Let n >1 be a positive integer. using the epsilon-delta definition of continuity, prove g(x)=[f(x)]^n is continuous as a Homework Equations i know how to do it as a sequence proof; but i don't know how to use the epislon/delta...
  20. T

    F(x) integral converge, f(x) uniformly continuous ,prove that f(x) limit = 0

    Homework Statement \int_{a}^\infty\ f(x) dx <--- converge f(x) uniformly continuous in [a,\infty] prove that lim_{x\rightarrow \infty} f(x) = 0 Homework Equations The Attempt at a Solution I know that if f(X) has a limit in \infty it has to be 0 I think that the...
  21. D

    Field Due to Continuous Distribution of Charge

    Homework Statement Coulomb force between line charges: a rod of length l1 with line charge density λ1 and a rod of length l2 with line charge density λ2 lie on the x axis. Their ends are separated by a distance D as shown in the figure. (a) What is the force F between these charges...
  22. J

    Proving Continuous Functions Cannot Be Two-to-One

    Homework Statement Suppose f: [0,1] \rightarrow R is two-to-one. That is, for each y \in R, f^{-1}({y}) is empty or contains exactly two points. Prove that no such function can be continuous. Homework Equations Definition of a continuous function: Suppose E \subset R and f: E...
  23. N

    Finding the Value of b to Make f Continuous at x=0

    f(x) = { [(e^x) - 1] / x ; if x not equal 0 ... .{ b ......; if x = 0 What value of b makes f continuous at x = 0? so.. the left side and right side must be equal in order to make f continuous at x = 0 [(e^x) - 1] / x = b [(e^x) - 1] = (b)(x) e^x = (b)(x) + 1 . . . dont know...
  24. N

    Determine whether the function f(x) is continuous

    Homework Statement Given that f(x) = { x + 1 ......; if x < 1 ...{ 2 .....; if x = 1 ...{ [4(x-1)] / (x^2 - 1) ; if x > 1 Determine whether the function f(x) is continuous at x = 1 i don't know how to start.. can someone give me an idea to start..
  25. D

    Electric Field due to Continuous Line Charge

    Homework Statement Find the electric field a distance z above the midpoint of a straight line segment of length 2L, which carries a uniform line charge λ. Homework Equations 1) my textbook says : E(r) = 1/4πεo ∫V λ(r')/r2 r dl' 2) and this also works? : E(r) = 1/4πεo ∫V λ(r')/r3...
  26. J

    Piecewise continuous - step function

    Homework Statement Consider the following initial value problem: y''+4y = 9t, 0<=t<2 ...0, t>=2 Find the equation you get by taking the Laplace transform of the differential equation and solve for Y(s) Homework Equations The Attempt at a Solution I am just having trouble with the step...
  27. A

    Is a Continuously Converging Function on [0,∞) Uniformly Continuous?

    Suppose f:[0,\infty]\rightarrow \mathbb{R} is a continuous function such that \lim_{x\rightarrow \infty} f(x)=1. I want to show that f is uniformly continuous. Thanks.
  28. G

    Find k for Continuous & Differentiable Function

    Homework Statement find k for the function so it is continuous and differentiable. x^2-1 x<=1 k(x-1) x>1 The Attempt at a Solution k(x-1)=0 for x=1 k(0)=0 k = 0/0? How do I know if the function is differentiable?
  29. C

    Prove function continuous at only one point

    Homework Statement Prove that the function defined as f(x)= x when x is rational and -x when x is irrational is only continuous at 0. Homework Equations The Attempt at a Solution I have been looking at this website which proves this...
  30. C

    Nowhere Continuous Function Dirichlet Proof

    Homework Statement Prove that the Dirichlet function is continuous nowhere. Homework Equations Dirichlet function = 1 when x is rational, and 0 when x is irrational. The Attempt at a Solution I was looking at this proof on http://math.feld.cvut.cz/mt/txtd/1/txe4da1c.htm At the...
  31. N

    Is the anti-derivative of a continuous function continuous?

    Hi guys I have been wondering: Say we have a continuous function f. I integrate f to obtain its anti-derivative called capital f, i.e. F. Now I wish to prove the differentiability of F, and in order to do so, I need the fact that F is continuous (this is just something I need in my proof)...
  32. C

    Summation of continuous band of frequencies

    Just got a "thought experiment" question from a colleague. The question, as phrased was: If an audio signal was composed by adding all of the frequencies in the audible range, what would it sound like? I thought it was interesting, so I attempted to solve it by integral. My calculus skills...
  33. Z

    Continuous function / epsilon-delta

    Homework Statement Let h: \Re \rightarrow \Re be a continuous function such that h(a)>0 for some a \in \Re. Prove that there exists a \delta >0 such that h(x)>0 provided that |x-a|< \delta . Homework Equations Continuity of h means that there exists and \epsilon >0 such that...
  34. W

    F: [0,infinity) -> R is continuous at every point of its domain

    Problem: Assume that f: [0,infinity) -> R is continuous at every point of its domain. Show that if there exists a b>0 so that f is uniformly continuous on the set [b,infinity) then f is uniformly continuous on [0,infinity). I don't really know where to start with this one, any help would...
  35. S

    Prove a function is not continuous

    Homework Statement Using the epsilon-delta definition, prove that the function f:R^{2} \rightarrow R by f(x,y) = xy/((x^{2}) + (y^{2})), and f(0,0) = 0 is not continuous. The Attempt at a Solution I just really have no clue how to set up a delta-epsilon proof for functions that involve...
  36. B

    Continuous expansion is surjective

    Homework Statement (X,d) a compact metric space, f:X->X cts fn, with d(f(x),f(y)) >= d(x,y) for all x, y in X Prove that f is a surjection.The Attempt at a Solution Let K be the set of points that are not in f(X). It is a union of open balls because X is closed and hence so is f(X). Choose...
  37. E

    Magnetic Fields: Continuous or Discontinuous?

    HI, A question which arises to me is about magnetic fields of a wire or a permanent magnet, Are they continuous? or are discontinuous like what we draw them when We want to show them in a paper? If they are continuous then why we see discontinuous lines when we make a test by iron's...
  38. M

    Continuous application of Lense-Thirring precession: flyby anomalies

    Not sure where to put this, but if it's wrong, sorry... I just looked at the Nieto, Anderson paper on arXiv: arXiv:0907.3418 "Earth Flyby Anomalies" Funnily enough, it's about anomalies in the velocity of probes doing Earth flybys! This has hit the scientific news (New Scientist this...
  39. D

    Continuous function and limits

    Homework Statement Consider a function f : R--> R, and assume that there is a c is in (0, 1) so that |f(x) - f(y)|<= c|x -y| for all x, y in R. (a) Show that f is continuous on R. (b) Given a point y1 in R de fine a sequence by yn+1 = f(yn). Prove that yn is a Cauchy sequence (and...
  40. K

    Does every continuous function has a power series expansion on a closed interval

    By Weierstrass approximation theorem, it seems to be obvious that every continuous function has a power expansion on a closed interval, but I'm not 100% sure about this. Is this genuinely true or there're some counterexamples?
  41. A

    Lagrangian mechanics of continuous systems

    I'm thinking about generalizations of Lagrangian mechanics to systems with infinitely many degrees of freedom, but what I've got uses some extremely sketchy math that still appears to give a correct result. I only consider conservative systems that do not explicitly depend on time. Of course...
  42. T

    How to Calculate the Probability of a Pump Failure in a Given Mile Range?

    I need help with this problem: KleerCo supplies an under-hood, emissions-control air pump to the automotive industry. The pump is vacuum powered and works while the engine is operating, cleaning the exhaust by pumping extra oxygen into the exhaust system. If a pump fails before the vehicle...
  43. C

    Proof about a real-valued continuous function?

    Proof about a real-valued continuous function?? Homework Statement Five line segments meet at a point. Show that any continuous real-valued function defined on this set must take the same value three times. The Attempt at a Solution Take the values f(0,0,0) f(0,0,1) f(1,0,0) f(0,1,0)...
  44. D

    Function f(x) such that it's continuous

    Am I correct - First...define the variables - x – Independent variable of the function f. l – The “limit” f(x). The value of l is is known, arbitrary and f(x) should be equal to l. a – a value such that f(a) = l δ – The value of x can be varied by a certain amount...δ is that...
  45. R

    Continuous Time Fourier Series of h(t)e^(-4|t|)

    1. Determine the Continuous Time Fourier Series representation of the response where: h(t)=e^(-4*|t|) and x(t)=summation n=-inf to inf of dirac(t-n) The attempt at a solution: I used Laplace transforms to find the frequency response: H(s) = 4/(16-s^2) from what I recall isn't the x(t)...
  46. L

    Proving Continuous Function: Epsilon-Delta Proof

    how do i show f(x)=\frac{x}{1-x^2} is a continuous function by means of an \epsilon - \delta proof? oh and x \in (-1,1) so far i have said: let \epsilon>0, \exists \delta>0 s.t. |x-x_0|< \delta. now i need to show that |f(x)-f(x_0)|< \epsilon. yes? can't do the rest of it though...
  47. L

    If f is differentiable, is f ' continuous?

    So, a certain discussion occurred in class today... If f is differentiable, is f ' continuous? At first sight, there seems no reason to think so. However, we couldn't think any counterexample. It also seems logical that f' is continuous since otherwise f wouldn't be differentiable. For...
  48. Q

    Discrete and continuous confusion

    I don't understand how in quantum mechanics we have discrete and exact energy states for electron orbits but then at the same time we have a continuous probability density function for the position of an electron. This seems like a paradox (although I know it can't be) since considering a...
  49. S

    Is Time Discrete or Continuous?

    Whether or not time is discrete or continuous is unknown, and is a key idea answer that many physicists are looking for. This topi is for discussing the factors that effects whether or not ime is continuous, and effects it might have. Before i talk about whether or not time is discrete or...
  50. F

    Prove Sin(x):R->R is continuous

    Prove Sin(x):R--->R is continuous Homework Statement Prove that Sin(x) from R to R is continuous using the epsilon delta definition of continuity and the following lemma: denote the absolute value of x by abs(x) Lemma: abs(x)>=sin(x) Homework Equations Could somebody please just...
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