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account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.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

    Function continuous or not at (0,0)

    Homework Statement f\rightarrowℝ, f(x,y)=\frac{x^{2}y}{x^{6}+y^{2}} where (x,y)\neq(0,0) and f(0,0)=0. Is the function continuous at (0,0)? The Attempt at a Solution I tried to find the limit at (0,0) so I put y=x into the function f and got the limit 0 when x\rightarrow0. Tthen I...
  2. W

    Effect of continuous refueling on decay heat

    Estimate the decay heat rate in a 3000 MWth reactor in which 3.2% mU-enriched U02 assemblies are being fed into the core. The burned-up fuel stays in the core for 3 years before being replaced. Consider two cases: 1. The core is replaced in two batches every 18 months. 2. The fuel...
  3. P

    A very basic question about continuous function

    Hello everyone, This is probably a really newbie question and I apologise for it. So a continuous function is one that is differentiable with respect to its input parameters. What happens when the input parameters can only take discrete values? So, I guess the function can, of course, not...
  4. T

    What Are the Values of c for Continuity at x=5?

    Homework Statement f(x) = x^2 - c^2 \mbox{ if } x < 5 f(x) = cx+11 \mbox{ if } x \geq 5 Find the two values of c for which the function would be continuous. Homework Equations The Attempt at a Solution I set these two equations equal to each other, plug in the value 5...
  5. A

    Electric field of Continuous charge Distribution

    A line of positive charge is formed into a semicircle of radius R = 57.8 cm, as shown in the figure below. (The figure is a semicircle above the x-axis with angle θ measured from positive y axis centred at the origin) The charge per unit length along the semicircle is described by the...
  6. J

    Equicontinuous sequences of functions vs. continuous functions

    Hello, below I have the problem and solution typed in Latex. For the first part, I just want someone to verify if I am correct. For the second part, I need guidance in the right direction
  7. M

    Test for continuous torque and peak torque.

    Hello, I want to test gearboxes. How do you recommend I test the continuous torque of a gearbox and also the peak torque of the gearbox? I want to test to see the maximum torque the gearbox can handle. How do you suggest I go about doing so? What type of equipments or measuring devices...
  8. I

    Prove directly that sqrt defined on [0,1] is uniformly continuous

    This is not a homework problem, but it may as well be, so I thought I'd post it here. Homework Statement The function f:[0,1] \to \mathbb{R} given by f(x)=\sqrt{x} is continuous on a compact domain, so it is uniformly continuous. Prove that f is uniformly continuous directly (with a...
  9. R

    Continuous and smooth on a compact set implies differentiability at a point

    I'm trying to prove that if a function is continuous on [a,b] and smooth on (a,b) then there's a point x in (a,b) where f'(x) exists. The definition of smoothness is: f is smooth at x iff \lim_{h \rightarrow 0} \frac{ f(x+h) + f(x-h) - 2f(x) }{ h } = 0 . I'm starting with the simpler case...
  10. U

    Orthogonal Complements of complex and continuous function subspaces

    Homework Statement I'm having a tough time figuring out just how to get the orthogonal complement of a space. The provlem gives two separate spaces: 1) span{(1,0,i,1),(0,1,1,-i)}, 2) All constant functions in V over the interval [a,b] Homework Equations I know that for a subspace W of an...
  11. S

    Applying ln to a graph: where would it be continuous?

    Homework Statement Homework Equations I'm looking over in old midterm to prepare for a final and can't figure out what the correct answer is. No answers were ever given. I'm not cheating on anything, would just like to know what the correct answer is and why :) The Attempt at a...
  12. M

    How Do You Find 'a' for P(-a ≤ X ≤ a) = 0.95?

    Hi all, I was having some troubles with a practise question and thought I'd ask here. Given an r.v. X has a pdf of f(x) = k(1-x2), where -1<x<1, I found k to be 3/4. And I found the c.d.f F(x) = 3/4 * (x - x3/3 + 2/3) Now I have to find a value a such that P(-a <= X <= a) = 0.95. I thought...
  13. A

    Continuous Function and Integral Proof

    Homework Statement Let f be a function such that: \left |f(u) - f(v) \right | \leq \left | u - v\right | for all 'u' and 'v' in an interval [a, b]. a) Prove that f is continuous at each point of [a, b] b) Assume that f is integrable on [a, b]. Prove that: \left | \int_{a}^{b}...
  14. N

    Analyzing a Continuous Decreasing Function: Critical Point at (4,2)

    Homework Statement Multiple Choice If f is a continuous, decreasing function on [0, 10] with a critical point at (4, 2), which of the following statements must be false? E (A) f (10) is an absolute minimum of f on [0, 10]. (B) f (4) is neither a relative maximum nor a relative minimum...
  15. D

    Reinforcement in continuous beams

    Homework Statement I have been asked to provide a detailed reinforcement plan for a continuous beam. This beam has the following dimensions: h=180mm, b=500mm and l=5400mm. The supports are three and located at 200 (roller), 2700 (pinned) and 5200 (roller)mm, creating two equal spans. The...
  16. H

    Help with continuous functions in metric spaces

    hi guys, I have a question I would like assistance with: let (v,||.||) be a norm space over ℝ, and let f:v→ℝ be a linear functional. if f is continuous on 0 (by the metric induced by the norm), prove that there is k>0 such that for each u in v, |f(u)| ≤ k*||u||. thanks :)
  17. S

    Is there an interesting way to define a continuous composition of functions?

    People have found ways to extend the definition of some operations that are ostensibly discrete (such as differentiation - e.g. 1st, 2nd, 3rd derivatives) to operations that are defined for fractions ( e.g. fractional derivatives). Is there an interesting way to extend the operation of...
  18. J

    Let f be a continuous real function on a metric space X. Let

    Homework Statement Let f be a continuous real function on a metric space X. Let Z(f) be the set of all p in X at which f(p) = 0. Prove that Z(f) is closed. Homework Equations Definition of continuity on a metric space. The Attempt at a Solution Proof. We'll show that X/Z(f) = {p...
  19. B

    Does there Exist a Continuous Map ?

    Hi, All: I saw this question somewhere else: we are given any two topological spaces (X,T), (X',T'), and we want to see if there is always at least one continuous map between the two. The idea to say yes is this: we only need to find f so that f-1(U)=V , for every U in T', and some V in T. So...
  20. N

    Real analysis: show that a continuous function is defined for irrationals

    Let f be a continuous function defined on (a, b). Supposed f(x)=0 for all rational numbers x in (a, b). Prove that f(x)=0 on (a, b). i don't even know where to start...any tips just to point me in the right direction?
  21. V

    Can continuous acceleration reach speed of light?

    Hi, May be a dumb question; imagine a hypothetical situation of a spaceship in space with no influence of gravity due to Earth or nearby moon. Assuming the spaceship has enough fuel, if it injects the fuels outwards, it will accelerate in the opposite direction. Now, the new velocity will be...
  22. P

    Show No Continuous Function (Complex Analysis)

    Let n ≥ 2 be a natural number. Show there is no continuous function q_n : ℂ → ℂ such that (q_n(z))^n = z for all z ∈ ℂ. The only value of this function we can deduce is q_n(0)=0. Moreover any branch cut we take in our complex plane will touch zero. These two facts would make me a bit...
  23. P

    Continuous Injective Function on Compact Set of C

    Prove that the inverse of a continuous injective function f:A -> ℂ on a compact domain A ⊂ ℂ is also continuous. So basically because we're in ℂ, A is closed and bounded, and since f is continuous, the range of f is also bounded. Given a z ∈ A, I can pick some arbitrary δ>0 and because f is...
  24. A

    Give me a function that is piecewise continuous but not piecewise smooth

    Give me a function that is piecewise continuous but not piecewise smooth
  25. T

    Continuous Function with Open Range

    What is an example of a continuous function f:\mathbb{R}\to\mathbb{R} such that f(\mathbb{R}) is open?
  26. F

    Continuous deformation? Family of curves? So confused

    I understand the concept behind continuous deformations. Say we have two curves ζ1 and ζ2 from A to B on some domain D and say that Pdx + Qdy is closed. Say we can show n points A=c1,c2,...,cn=B and A=d1,d2,d3,...,dn=B, so that we can first say follow the curve ζ1 from A to c1 then over to...
  27. T

    Using the definition of continuity prove a function is continuous.?

    Homework Statement Using the definition of continuity, prove that the function f(x) = sin x is continuous. Hint: sin a − sin b = 2 sin (a-b)/2 . cos (a+b)/2Homework EquationsThe Attempt at a Solution Using the idea that: |sin(x)| ≤ |x| |cos(x)| ≤ 1 along with the hint: sin a − sin b = 2...
  28. A

    Show that f Uniform Differentiable implies f' Uniform Continuous

    Homework Statement A function f:(a,b)\to R is said to be uniformly differentiable iff f is differentiable on (a,b) and for each \epsilon > 0, there is a \delta > 0 such that 0 < |x - y| < \delta and x,y \in (a,b) imply that \left|\frac{f(x) - f(y)}{x - y}-f'(x)\right| < \epsilon. Prove that...
  29. J

    Comparing Continuous Probability Distributions: Finding Significance

    Hi, I was searching the forum about comparing continuous probability distributions and came across this post back in 2005. "You could make two variables X(t) = value of the "true" disrtibution (expensive simulation) at point t and Y(t) = value of the alternative dist. (practical simulation)...
  30. J

    Oversampling/undersampling of a continuous time signal and preventing aliasing

    Hi everyone, I want to understand how these concepts work. Suppose that we have a signal x(t) which has a maximum frequency component of 3 Hz. So let the DTFT of this signal be like that: http://img341.imageshack.us/img341/1134/31096081.png Also let y[n] be the digital signal that we get...
  31. G

    Abs Continuous Function w/ Unbounded Derivative on [a,b]

    What is an example of an absolutely continuous function on [a,b] whose derivative is unbounded? I know that the function f: [-1,1] defined by f(x) = x^2sin(1/x^2) for x ≠ 0, f(0) = 0 is continuous and its derivative f'(x) = 2xsin(1/x^2)-2/xcos(1/x^2) for x ≠ 0, f'(0) = 0 is unbounded on...
  32. G

    Absolutely continuous functions and sets of measure 0.

    Homework Statement Prove that if f: [a,b] -> R is absolutely continuous, and E ∁ [a,b] has measure zero, then f(E) has measure zero. Homework Equations A function f: [a,b] -> R is absolutely continuous if for every ε > 0 there is an δ > 0 such that for every finite sequence {(xj,xj')}...
  33. L

    Inner product space of continuous function

    Homework Statement C[a,b] is a vector space of continuos real valued functions. for f,g in C[a,b] <f,g>=∫f(x)g(x)dx, [a,b] Give a completely rigorous proof that if <f,f>=0, then f=0 2. The attempt at a solution I tried to prove this by contrapositive, "f≠0 implies that <f,f>≠0 When...
  34. jinksys

    Representing |psi> with Continuous Eigenvectors: An Example

    Homework Statement for discrete basis vectors {{e_n}}, a state vector |psi> is represented by a column vector, with elements being psi_n = <e_n|psi>. When basis vectors correspond to those with continuous eigenvalues, vectors are represented by functions. Give such an example of a state...
  35. S

    Continuous Functions, IVT/EVT?

    Homework Statement Suppose that f(x) is a continuous function on [0,2] with f(0) = f(2). Show that there is a value of x in [0,1] such that f(x) = f(x+1). Homework Equations Intermediate Value Theorem? Extreme Value Theorem? Periodicity? The Attempt at a Solution For sure there's an...
  36. G

    Exploring the Continuous Spectrum of Ordinary Light Bulbs

    hi i was wondering why the spectrum of an ordinary light bulb is continuous. i know that "i think it's thermodynamics" says that some temperature creates a specific continuous radiation, but how is this reconcilable with quantum mechanics and e.g. a sodium gas, that emits only a tiny yellow...
  37. A

    Is that subset of the set of continuous differential functions closed?

    Hi! I have used the physics forum a lot of times to deal with several tasks that I had and now its the time to introduce my own query! So please bear with me :-) Homework Statement Equip the set C^1_{[0,1]} with the inner product: \left\langle f,g \right\rangle= \int_{0}^{1}...
  38. L

    Analysis of Continuous functions

    Homework Statement Let f : R → R be continuous on R and assume that P = {x ∈ R : f(x) > 0} is non-empty. Prove that for any x0 ∈ P there exists a neighborhood Vδ(x0) ⊆ P. Homework Equations The Attempt at a Solution If you choose some x, y ∈ P, since f(x) is continuous then |f(x)...
  39. Shackleford

    Analysis: Continuous Functions

    I did the work. I'm not sure on some of these. I think for (c) I need to make D = (0, infinity) http://i111.photobucket.com/albums/n149/camarolt4z28/1-3.png http://i111.photobucket.com/albums/n149/camarolt4z28/2-3.png http://i111.photobucket.com/albums/n149/camarolt4z28/3-1.png
  40. M

    Find f'(0), if it exists and is f continuous at x=0

    *couldn't edit the title so Find* Homework Statement f(x) = x+1 , x<0 f(x) = 1 , x=0 f(x)= x2-2x+1 , x>0 The Attempt at a Solution for a (find f'(0), if it exists) i did as followed Lim h->0- (x+h)+1-(x) /h giving me in the end 1 as for the third equation, I did...
  41. J

    Continuous Function? g(x): Real Q & Non-Q Cases

    let g:R->R be a real function defined by rule g(x) = x^2 if x\in\mathbb{Q} and g(x) = 0 if x\notin\mathbb{Q} is g continuous (*on R)? Many thanks in advance *thanks for pointing out mistake above.
  42. A

    Motive behind the proof in f(x+y)=f(x)+f(y) is continuous

    Homework Statement The problem is: Suppose f is a function with the property f(x+y)=f(x)+f(y) for x,y in the reals. suppose f is continuous at 0. show f is continuous everywhere. I saw this post as an alternative solution that doesn't use epsilon-delta...
  43. M

    Function continuous, then a subset is closed

    Homework Statement Let M, N be two metric spaces. For f: M --> N, define the function on M, graph(f) = {(x,f(x)) \inMxN: x\inM} show f continuous => graph(f) is closed in MxN Homework Equations The Attempt at a Solution I can't figure out what method to use. I have...
  44. K

    Show that a uniformly continuous function on a bounded, open interval is bounded

    Homework Statement Suppose that the function f|(a,b)→ℝ is uniformly continuous. Prove that f|(a,b)→ℝ is bounded. Homework Equations A function f|D→ℝ is uniformly continuous provided that whenever {un} and {vn} are sequences in D such that lim (n→∞) [un-vn] = 0, then lim (n→∞) [f(un) -...
  45. A

    Please help on arithmetic mean of continuous distributions.

    PROVE mean (X bar) of a continuous distribution is given by: ∫x.f(x)dx {'a' is the lower limit of integration and 'b' is the upper limit}
  46. A

    Show that f is continuous at every point in R

    Suppose a function f : R → R satisfy f(x + y) = f(x) + f(y) and f is continuous at x = 0: Show that f is continuous at every point in R. (Hint: Using the fact that lim f(x) = l implies x→x0 limf(x0+h)= l h→0 )
  47. C

    Density function for continuous random variables

    For the density function for random variable Y: f(y) = cy^2 for 0<= y <= 2; 0 elsewhere We are asked to find the value of c. I did a definite integral from 0 to 2 of cy^2. I get c = 3/8. Why would the book show an answer of c = 1/8? Is this an error on their part or am I missing something...
  48. T

    Weak limit of abs. continuous measures

    say we have a sequence of probability measures on R, such that each one is abs. continuous wrt the Lebesgue measure... is it possible that these measures converge weakly to a measure which is _not_ abs. continuous wrt the Lebesgue measure?
  49. srfriggen

    The set of all continuous functions

    I suppose my question is, "does the set of all continuous functions comprise a continuum?" How would one even start at trying to prove that? Any ideas or suggestions?
  50. I

    How Do Continuous and Discrete Signals Get Processed in Biomedical Engineering?

    Name 5 signals and the systems that process them. – Draw the block diagrams to show how the signal gets transformed. • Choose both Continuous and Discrete signal • Include some examples from Bio Medical Engineering.
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