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account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.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

    Proof involving means in continuous distributions

    I recall reading somewhere that the mean value of a continuous variable is situated at a point that acts as a fulcrum about which all other values are considered "weights". In other words, if we define the mean as μ = \int^{∞}_{-∞} x ρ(x) dx (where rho is the probability density) then...
  2. J

    Continuous random variable (supply and demand)

    Homework Statement In the winter, the monthly demand in tonnes, for solid fuel from a coal merchant may be modeled by the continuous random variable X with probability density function given by: f(x)=\frac{x}{30} 0≤x<6 f(x)=\frac{(12-x)^{2}}{180} 6≤x≤12 f(x)=0 otherwise (a)...
  3. C

    Is space currently thought of as discrete or continuous?

    I was wondering what the majority opinion was on this issue, among physicists and philosophers as well. I can't imagine zooming in a million times smaller than the plank length and still not being at a smallest length, however a discrete universe doesn't make much sense to me. Are there any...
  4. N

    Continuous matrix = differential operator?

    Hello, Sorry if the question sounds silly, but can a continuous matrix be seen as a differential operator? First of all, let me state that I have no idea what a continuous matrix would formally mean, but I would suppose there is such an abstract notion, somewhere? Secondly, let me tell...
  5. V

    Simple continuous tracking radar system with cantenna - how to get ranging info?

    Simple continuous tracking radar system with cantenna We are in need of a simple radar target tracking signal processing method. It's to be very short range, less than 5 meters. It needs to track a single target that can be moving or stationary at any time. We are using 2.4 GHz ISM band...
  6. L

    Prove f continuous given IVP and 1-1

    Homework Statement Let f : (-1, 1) → ℝ. f satisfies the intermediate value property and is one-to-one on (-1, 1). Prove f is continuous on (-1, 1) The Attempt at a Solution I was thinking that the IVP and one-to-one implies that f should be strictly monotonic and that a strictly monotonic...
  7. E

    Find the value of p and q that make the function continuous

    Homework Statement Find the value of p and q that make the function continuous Homework Equations f(x)= x-2 if x≥2 \sqrt{p-x^{2}} -2<x<2 q-x if x≤-2 The Attempt at a Solution lim f(x)= x-2 n→2+ lim f(x)=q-x n→-2 I really have no idea how to continue,the teacher never explained this and I...
  8. H

    Association between nominal and continuous variables

    Suppose you have two random samples of the profit margins obtained by two stock traders, Trader A and Trader B. The first data set consists of 18 data, and the second has 21. I want to check if there is association between the variables "type of trader" (values A or B) and "profit margin"...
  9. K

    Fourier Coefficients of Continuous functions are square summable.

    Homework Statement If C^1(\mathbb T) denotes the space of continuously differentiable functions on the circle and f \in C^1(\mathbb T) show that \sum_{n\in\mathbb Z} n^2 |\hat f(n)|^2 < \infty where \hat f(n) is the Fourier coefficient of f. The Attempt at a Solution Since f is...
  10. E

    Suppose that f is continuous function on the interval [a,b]

    Suppose that f is continuous function on the interval [a,b] integral from b to a If(x)I dx =0 if and only if f(x)=0 for all x in [a,b] ıs it true or false ? ı can prove that if f is zero,integral is zero but ı can,'t do that if integral is zero f is zero Regards
  11. E

    Continuous functions on dense subsets

    Hi, can someone give me pointers on this question Homework Statement Prove or provide a counterexample: If f : E -> Y is continuous on a dense subset E of a metric space X, then there is a continuous function g: X -> Y such that g(z) = f(z) for all z element of E. The Attempt at a Solution...
  12. M

    Proving Constant Function f: X → Y is Continuous

    Hi, can someone please check if my proof is correct 1. a) Assume f : R -> R is continuous when the usual topology on R is used in the domain and the discrete topology on R is used in the range. Show that f must be a constant function. My attempt : Let f: R --> R be continuous. Suppose...
  13. johann1301

    Spacetime: continuous or quantized?

    What proof or evidence -both theoretical or emperical - is there, that spacetime is quantized or continuous?
  14. R

    Managing Continuous Operation of Flame Machine with Sleep Function

    Hi, I am correcting a C code which was written for a flame machine. My desire is to give a burst cool time when the machine working continuously. In deep, user could have the facility to enter the flame time and cool time before a continuous operation. So, i exactly want to off the...
  15. M

    Continuous Inelastic Collisions

    Hi, I am trying find equations for continuous "stretchy" collisions, in other words, I have two perfectly round objects of known mass, radius, and velocity, and want to collide them and be able to have them squish together and then bounce apart. I am aware of the method of solving for the...
  16. F

    Servo motor: what is the continuous servo motor?

    Hello Forum, there are two typeos of servo motors. One of them is called continuous. does it mean that it can rotate to any angular position, between 0 degrees and 360? The other type (the non continuous one) still rotates at any angular position, but only within a limited range, like 0 to...
  17. M

    Is f Continuous on ℝ if Continuous on a Dense Subset?

    Homework Statement T or F, If f:ℝ→ℝ is continuous on a dense set of points in ℝ, then f is continuous on ℝ. Homework Equations definition of continuity using sequences, maybe? The Attempt at a Solution false. Take f(x)= {1 if x\in Q(rational numbers) and 0 if x\in...
  18. B

    Show f is continuous if the range of f is a bounded interval

    Homework Statement Show that if f: [a,b]→Re is increasing and the range of f is a bounded interval then f is continuous. Homework Equations N/A The Attempt at a Solution I have no idea where to start, but I decided to start with a couple of things. Proof: Let f: [a,b]→Re...
  19. I

    Why Continuous Functions Don't Preserve Cauchy Sequences

    Homework Statement Why is it that continuous functions do not necessarily preserve cauchy sequences. Homework Equations Epsilon delta definition of continuity Sequential Characterisation of continuity The Attempt at a Solution I can't see why the proof that uniformly continuous...
  20. N

    Finding CDF for Continuous RVs problem

    Homework Statement I'm given the pdf and asked to find F(y)/ cdf. I've calculated it many times, but I'm not getting the right numbers. the pdf is f(y)= .5, ....-2≤y≤0 .75-.25y,...1≤y≤3 0,...elsewhere so that means f(y)= 0,...y< -2 0.5, ...-2≤y≤0...
  21. H

    Prove a function is continuous at a point (2)

    As in my previous thread we had: "Let f a function which satisfies $$|f(x)|\leq|x| \forall{x\in{\mathbb{R}}}$$ Proof that is continuous at 0. We concluded that since f(0)=0 then we found a delta equal epsilon so $$|f(x)|≤|x|<ϵ$$. But now I have: $$\textrm{g continuous at 0 and...
  22. K

    Difference between Uniformally Continuous and Continuous

    I don't see the subtle differences between continuous and uniformally continuous functions. What can continuous functinons do that unifiormally continuous functions can't or vice versa?
  23. R

    Finding the prob. in a continuous uniform distribution (z values)

    Homework Statement Homework Equations The Attempt at a Solution I understand that all i need to do is plug these two points into the formula and subtract to get the correct area, but i am not provided a mean or variance as i normally am, so I'm at a loss.
  24. K

    Continuous functions on intervals

    Homework Statement Suppose that f : ℝ→ℝ is continuous on ℝ and that lim f =0 as x→ -∞ and lim f =0 as x→∞. Prove that f is bounded on ℝ and attains either a maximum or minimum on ℝ. Give an example to show both a maximum and a minimum need not be attained. The Attempt at a Solution...
  25. K

    Continuous Functions: Uniform Continuity

    Homework Statement Let f be continuous on the interval [0,1] to ℝ and such that f(0) = f(1). Prove that there exists a point c in [0,1/2] such that f(c) = f(c+1/2). Conclude there are, at any time, antipodal points on the Earth's equator that have the same temperature. Homework Equations...
  26. M

    MHB Proving Uniqueness of Fourier Coefficients for Continuous Periodic Functions

    Let $f:\mathbb R\to\mathbb R$ be a continuous function of period $2\pi.$ Prove that if $\displaystyle\int_0^{2\pi}f(x)\cos(nx)\,dx=0$ for $n=0,1,\ldots$ and $\displaystyle\int_0^{2\pi}f(x)\sin(nx)\,dx=0$ for $n=1,2,\ldots,$ then $f(x)=0$ for all $x\in\mathbb R.$ I know this has to do with the...
  27. T

    General question regarding continuous functions and spaces

    Let X be some topological space. Let A be a subspace of X. I am thinking about the following: If f is a cts function from X to X, and g a cts function from X to A, when is the piece-wise function h(x) = f(x) if x is not in A, g(x) if x is in A continuous? My intuition tells me they must agree...
  28. K

    Combinations of Continuous Functions

    Homework Statement Let g: ℝ→ℝ satisfy the relation g (x+y) = g(x)g(y) for all x, y in ℝ. if g is continuous at x =0 then g is continuous at every point of ℝ. Homework Equations The Attempt at a Solution Let W be an ε-neighborhood of g(0). Since g is continuous at 0, there is...
  29. A

    MHB Quick question about continuous mapping

    When f maps E into a metric space Y: (E is subset of metric space X) Is it eqivalent to say that f is a continuous mapping and that for a subset E of X, to say that for every p element of E, f is continuous at p.? thank you
  30. B

    Cardinality of the Preimage f^{-1}(y) of f:X->Y continuous?

    Cardinality of the Preimage f^{-1}(y) of f:X-->Y continuous? Hi, All: Let X,Y be topological spaces and f:X-->Y non-constant continuous function. I'm curious as to whether it is possible for the fiber {f^{-1}(y)} of some y in Y to be uncountable, given that the fiber is discrete (this...
  31. I

    Is Function f Continuous at x=0?

    Homework Statement Define f:[-1,∞]→ℝ as follows: f(0) = 1/2 and f(x) =[(1 + x)^(1/2) - 1]/x , if x ≠ 0 Show that f is continuous at 0. Homework Equations Definition. f is continuous at xo if xoan element of domain and lf(x) - f(xo)l < ε whenever lx - xol < δ The Attempt at...
  32. J

    Is every empty set function continuous?

    Can I use the definition of continuity of function from Baby Rudin, setting X as empty set? Rudin does not specify X is a non-empty set but he supposes p is in X. Anyway if I use it for empty set X, then is a function with a domain E which is a subset of X continuous at p? One more...
  33. A

    Bounded continous implies uniformly continuous

    I'm trying to show that continuous f : [a, b] -> R implies f uniformly continuous. f continuous if for all e > 0, x in [a, b], there exists d > 0 such that for all y in [a, b], ¦x - y¦ < d implies ¦f(x) - f(y)¦ < e. f uniformly continuous if for all e > 0, there exists d > 0 such that for...
  34. M

    Proving a function is well defined and continuous

    Homework Statement Let f_{n}(x)=\frac{-x^2+2x-2x/n+n-1+2/n-1/n^2}{(n ln(n))^2} Prove f(x) = \sum^{\infty}_{n=1} f_{n}(x) is well defined and continuous on the interval [0,1]. Homework Equations In a complete normed space, if \sum x_{k}converges absolutely, then it converges.The Attempt at...
  35. J

    Is Space Continuous or Quantized?

    or is space itseld quantized meaning an object moving from a to b would in some way look like A \/\/\/\/\0/\/\/\/ B or is it smooth and continuous like A--------0------B ?
  36. F

    Continuous Functions: Does f(x+δ) = ε?

    A function defined on ℝ is continuous at x if given ε, there is a δ such that |f(x)-f(y)|<ε whenever |x-y|<δ. Does this imply that f(x+δ)-f(x)=ε? The definition only deals with open intervals so i am not sure about this. If this is not true could someone please show me a counter example for it...
  37. F

    Is the Function F(x) Continuous on ℝ for Any Value of a?

    Homework Statement assume a function F(x)=(a|x|^(a-1))*(sin(1/x))-((|x|^a)/(x^2))*(cos(1/x)) for x not equal to 0 F(x)=0 for x equal to 0 for what values of a that this function is continuous on R(real number) Homework Equations the F(x) is the differentiation of |x|^a sin(1/x)...
  38. F

    Continuous and differentiable function

    function f:R->R can be written as a sum f=f1+f2 where f1 is even and f2 is odd。then if f is continuous then f1 and f2 may be chosen continuous, and if f is differentiable then f1 and f2 can be chosen differentiable i am quiet confusing this statement , if f1 is continuous f2 is not how their...
  39. F

    Continuous and differentiable function

    Homework Statement function f:R->R can be written as a sum f=f1+f2 where f1 is even and f2 is odd。show that if f is continuous then f1 and f2 may be chosen continuous, and if f is differentiable then f1 and f2 can be chosen differentiable 2. The attempt at a solution i have try some...
  40. M

    Continuous not bounded above function

    Homework Statement Let f : R -> R be a continuous function such that f(0) = 0. If S := {f(x) | x in R} is not bounded above, prove that [0, infinity) ⊆ S (that is, S contains all non-negative real numbers). Then find an appropriate value for a in the Intermediate Value theorem...
  41. R

    What motor to use for vaccum continuous operation (12V DC)

    I need help on alternative motor that I can use for vacuum that can run continuously for 20 hours a day and it should be 12VDC powered. Basically I am doing a heat exhaust system for a data center. I want to use small pipes so it won't be bulky about 1.5" and for that to work I think strong...
  42. N

    [topology] The metric topology is the coarsest that makes the metric continuous

    [topology] "The metric topology is the coarsest that makes the metric continuous" Homework Statement Let (X,d) be a metric space. Show that the topology on X induced by the metric d is the coarsest topology on X such that d: X \times X \to \mathbb R is continuous (for the product topology on X...
  43. T

    Sequences and continuous functions

    Homework Statement a) Let {s_{n}} and {t_{n}} be two sequences converging to s and t. Suppose that s_{n} < (1+\frac{1}{n})t_{n} Show that s \leqt. b) Let f, g be continuous functions in the interval [a, b]. If f(x)>g(x) for all x\in[a, b], then show that there exists a positive real z>1 such...
  44. S

    MHB Finding a value that will make a function continuous

    Hi All, just a question regarding continuous functions. From what I understand if x > 2, then any value of 'a' should make this function continuous? Any clarification would be very helpful! Thanks in advance!
  45. Loren Booda

    Binary vs. continuous data outcomes

    On the average, which provides more information: yes/no answers or answers neither yes nor no? Just asking.
  46. T

    Proving Identity of Continuous Functions on Q

    Homework Statement Let f and g be two continuous functions defined on R. I'm looking to prove the fact that if they agree on Q, then f and g are identical. Homework Equations The Attempt at a Solution I'm not really sure where to start with this. Can someone point me in the right...
  47. T

    Continuous Surface Charge Source - Integral Confusion

    1. Homework Statement Find the total charge on a circular disc of radius ρ = a if the charge density is given by ρs = ρs0 (e^−ρ) sin2 φ C/m2 where ρs0 is a constant. Are the two limits of integration from 0 -> a for ρ and 0->2∏ for φ? In the example given in the notes, ρ varies, instead of...
  48. T

    What is the charge on a circular disc with a varying charge density?

    Homework Statement Find the total charge on a circular disc of radius ρ = a if the charge density is given by ρs = ρs0 (e^−ρ) sin2 φ C/m2 where ρs0 is a constant. Are the two limits of integration from 0 -> a for ρ and 0->2∏ for φ? In the example given in the notes, ρ varies, instead of...
  49. P

    Formula for the Electric Field Due to Continuous Charge Distribution

    Homework Statement I am having trouble understanding how \textit{Δ}\vec{E}\textit{ = k}_{e}\frac{Δq}{{r}^{2}} (where ΔE is the electric field of the small piece of charge Δq) turns into \vec{E}\textit{ = k}_{e}\sum_{i}\frac{{Δq}_{i}}{{{r}_{i}}^{2}} then into \vec{E}\textit{ =...
  50. M

    Continuous Probability Distribution Question

    Homework Statement Homework Equations The Attempt at a Solution I can show the second one, i.e. 1/3 [sqrt(y) +1] and need help in showing the first one. Can anyone guide me?
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