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account at time t would be considered discontinuous, since it "jumps" at each point in time when money is deposited or withdrawn.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

    Finding Positive Values of b for Continuous Function

    Homework Statement For what positive values of b is f continuous for all real numbers x? f(x) = ((x-1)(x2-4))/(x2-b) So I go one value of b for the function to be continuous. I got that b=4. How do I find any others? If there even are any others?
  2. M

    Set theory and analysis: Cardinality of continuous functions from R to R

    Homework Statement Prove the set of continuous functions from R to R has the same cardinality as RHomework Equations We haven't done anything with cardinal numbers (and we won't), so my only tools are the definition of cardinality and the Schroeder-Bernstein theorem and its consequences. I...
  3. L

    Continuous Function Problems AP Calculus

    Homework Statement Let f be the function given by f(x)= (x-1)(x²-4)/ (x²-a). For What Positive Values of a is f continuous for all real numbers x? Homework Equations The Attempt at a Solution What I tried doing was separating the (x²-4) into (x+2)(x-2) then moving along from...
  4. J

    Finding a and b for Continuous f(x) at x=0

    Homework Statement Let \[f(x)=\begin{cases}{} \frac{6a(x^2+1)}{2x^2+1}+\frac{b\log \big((x+1)^4\big)}{x} &\mbox{if } x<0,\\ -2a-4 &\mbox{if } x=0, \\ \frac{a\sin x}{x}+b &\mbox{if } x>0. \end{cases}\] Find \(a\) and \(b\) such that \(f\) is continuous at \(x=0\). Homework...
  5. marcus

    Geometry both discrete and continuous at once, like information-Kempf

    Geometry both discrete and continuous at once, like information--Kempf It is possible for a geometry to be both discrete and continuous. We don't know if our universe's geometry is like that, but it could be. Video of a talk at Perimeter by Achim Kempf, describing this, was put online...
  6. S

    Find g(4) When f(4)-5 and lim[5f(x)-g(x)]=5

    If f and g are continuous functions with f(4)-5 and lim [5f(x) -g(x) ]=5 find g(4) x-->4
  7. O

    When Are Partial Derivatives Continuous?

    Hallo, What is the condition for partial derivatives to be continuous (if I have function f(x,y))? Thanks, Omri
  8. J

    Can Humans Learn From Fruit Flies to Ensure Their Own Survival on Earth?

    Hello, I would like to get an opinion from somebody on a theory I find interesting. If a fruit fly were to live in a house; and only discreetly eat that which is necessary for survival, It is possible that it could remain unnoticed to a point where it may live comfortable for the rest of its...
  9. C

    Someone help. Sequence and continuous functions.

    I am confused with sequence and continuous functions. I am confued with their limit. how do they know the min and max before they attempt the question. and is that the only solution to the question? I mean. Everytimes if I see kind question like this, is that only way to do it?... Many...
  10. A

    Dirac delta function is continuous and differential

    since dirac delta function is not a literally a function but a limit of function,does it mean that dirac delta function is continuous and differentiable through out the infinity? is there any example of dirac delta function if yes then give meeeeeeee?
  11. J

    Convergent Filter Base and Continuous Function

    Hi All, I can't see how the following is proved. Given two topological space (X, T), (Y, U) and a function f from X to Y and the following two statements. 1. f is continuous, i.e. for every open set U in U, the inverse image f-1(U) is in T 2. For every convergent filter base F -> x, the...
  12. F

    Periodic, continuous and piecewise smooth function

    Dear friends, I am a new member of physics forums, so this is may new message. Already thanks to you for your helps to my question. I research some applied mathematician problem's numerical solutions. There are initial-boundary value problems. I need an initial condition function which must...
  13. L

    Bijective & continuous -> differentiable?

    Is a bijective continuous function:[a,b]->[f(a),f(b)] differentiable? I think it has to be. continuity between two distinct values of f(a) and f(b): it got to take all the values between f(a) and f(b) at x in [a,b], by the intermediate value theorem. if f is bijective, at [a,b], f(x) can't go...
  14. F

    Prove that the bth projection map is continuous and open.

    I am trying to prove that the bth projection map Pb:\PiXa --> Xb is both continuous and open. I have already done the problem but I would like to check it. 1) Continuity: Consider an open set Ub in Xb, then Pb-1(Ub) is an element of the base for the Tychonoff topology on \PiXa. Thus, Pb is...
  15. T

    Continuous fibre reinforced polymer

    Homework Statement For a continuous fibre reinforced polymer, use a diagram to explain how the Young's modulus of the composite varies with fibre orientation and fibre content. Anywhere i could get any of this information? I've been googling with no success for a while
  16. B

    Proving that 1/(x+1) is continuous at x=0 using epsilon-delta def.

    As the thread title. The question is actually: "Given p > 0, find d so that |x-0| < d implies |f(x)-1| < p and hence deduce that f(x) approaches 1 as x approaches 0." My problem is that, when x is near the point x=0, x can be positive and negative, I don't know how to get my delta value because...
  17. J

    Is Signal Power Calculated Correctly in Pattern Recognition?

    I am doing some pattern recognition research. I have found that a signal power is an important variable in this field of study. However the continuous part of the spectrum (frequency = 0) isn't, and it must be discarded. As a software developer I have wrote computer methods to calculate the...
  18. R

    Why k in E(k) diagram continuous?

    i am wondering why k in E(k) diagram is continuous? How is it related to discrete reciprocal lattice which are Fourier components? richard
  19. S

    Convert Continuous Inverse Scale Parameter to Physically Relevant Units

    How to convert a continuous inverse scale parameter into a physically relevant quantity: 1) What is a CISP, and why is called continuous and why inverse? 2) how do I deal with it: Example: On http://www.apec.umn.edu/faculty/gpederso/documents/4501/risk45DistFunc.pdf the error function is...
  20. S

    How Can I Modify My Equation to Become a Continuous-Time Function?

    Lets say I have an equation, y=\alpha e^{\beta W} where, \alpha = a e^{b f} and \beta = c f + d W = \int^{T}_{0}f dt My problem now is, what happen if f is changing with time t, f(t) How do I modify my main equation, y, so that it become an continuous-time function, y(t)...
  21. T

    Show f is differentiable but partial derivatives are not continuous

    Homework Statement Define f: Rn --------> R as f(x) = (||x||^2)*sin (1/||x||) for ||x|| ≠ 0 f(x) = 0 for ||x|| = 0 Show that f is differentiable everywhere but that the partial derivatives are not continuous. Homework Equations The Attempt at a Solution Showing that it is...
  22. J

    Proving Continuity: When Does a Continuous Function Equal Zero?

    Homework Statement A subset of A \subseteq R of real numbers is called dense if \forall \delta > 0 , \forall x \in R , \exists a \in A: |x-a| < \delta . Suppose A \subseteq R is dense. Prove that if g is a continuous function with g(x) = 0 for all x \in A , then g = 0 Homework...
  23. J

    Is the Infinite Sum of Continuous Functions Also Continuous?

    Homework Statement Prove that the function f(x) = \sum_{n=1}^{\infty} \frac{cos(n^2x)}{e^{nx^2}2^n} is continuous on R. Homework Equations The Attempt at a Solution I haven't learned about a series of functions converging to a function yet, but would it be sufficient to show...
  24. K

    Continuous Function Homework: Determine & Sketch

    Homework Statement Determine whether the function is continuous, piecewise continuous or neither on the segment [0, 10] and sketch the graph of f(t). f(t)= {10-t, 0<=t<=8 and 10, 8<=t<=10) The Attempt at a Solution I would say that it was neither as the right hand limit at t = 8...
  25. C

    Proof of f(x) = g(x) for all x in R

    [b]1. Suppose that f and g are continuous functions defined on R and every interval (a, b) contains some point y with f(y) = g(y). Show that f(x) = g(x) for every x in R. [b]3. I can show that between any two points in are there is some x such that f(x)=g(x). Is that enough? I don't think...
  26. D

    Understanding Continuous Space, Spectra, and Planck Units in Quantum Spacetime

    How are continuous space and continuous spectra of operators mathematically consistent with Planck units? Shouldn't the quantum spacetime be a lattice (or what have you) of integer multiples of the Planck length?
  27. J

    When is the Inverse of a Continuous Bijection Continuous?

    Under which conditions is an inverse of a continuous bijection continuous? I'm not seeking for "the" answer. There probably are many. But anyway, I'm interested to hear about conditions that can be used to guarantee the continuity of the inverse. So far I don't know anything else than the...
  28. A

    Mathematica FFT, Mathematica, Continuous Fourier Transform

    Hi all, First a warning: my Mathematica skills, and computery-type skills in general, are not very hot. My problem is thus: I have a function which I know: \hat{f}(k) I'd like mathematica to approximate the inverse Fourier transform of this function for me and plot the result. I've...
  29. J

    Proving f(x) = 5^x for all real x using the epsilon-delta definition of limit

    Homework Statement Suppose f is continuous, f(1) = 5, and f(nx) = [f(x)]^n where n is any integer and x is any real number. Prove that f(x) = 5^x for all real x.Homework Equations The Attempt at a Solution I've proved that f(x) = 5^x for rational x. Now I have to extend this to irrational x...
  30. P

    Solve Continuous Function Homework: Render Graphic & Proof h: [0,1]→R

    Homework Statement Do the graphic rendering (and write the full proof) of the function h : [0,1) -> \Re , which is continuous and bounded but does not reach it's bounds. 2. The attempt at a solution If h is continuous : exists lim h(x) = h(x0) x->xo If h is bounded: А ≤ h(x) ≤ В for...
  31. H

    Proving Strictly Increasing Derivative with Continuous Function at a Point

    Homework Statement Suppose f is differentiable on J, c is in J0 and f'(c) > 0. Show that if f' is continuous at c, then f is strictly increasing on some neighborhood of c Homework Equations Strictly increasing: If x < y then f(x) < f(y) Continuous: For all epsilon > 0 there exists a...
  32. djeitnstine

    Transforming piecewise continuous functions

    I was just reflecting upon my math courses and wondered why can we transform any piecewise continuous functions by using transforms such as laplace transforms or converting to Fourier series by simply adding the required integrals on the respective bounds?
  33. V

    Help with continuous cooling diagrams

    I have the answers to these, but I have a question about them. The answers to 1 are P,P,M+P,M , and the answers to 2 are F+P,A+B+F+M+P,A+B+F+M,A+B+M,A+M . My question is, how come some of the answers to 2 have austenite, while none of the answers to 1 do? I don't see a Mfinish line...
  34. H

    Expectation of a Joint Continuous rv

    fx,y = 6(x-y)dydx, if 0<y<x<1 how do you find E(XY), i know the formula...g(x,y)fxy(x,y)dydx but i don't know what 'g(x,y)' represents and the limits to use??
  35. S

    Can a Positive Continuous Function Integrate to Zero?

    Suppose that f: [a,b] \rightarrow \mathbb{R} is continuous and f(x) \geq 0 for all x \in [a,b]. Prove that if \int^b_a f(x)dx=0, then f(x)=0 for all x \in [a,b]. Attempt I had attempted to do this problem by contradiction, except I did not understand how to finish the problem. I would...
  36. A

    Showing that wave functions are continuous

    Hello, In my QM class last semester, I produced a proof that wave functions must be continuous (used for boundary conditions, etc.) It was an undergraduate level course, so I don't know how easy it would be to do if you had more in the way of theory... But I've been wondering lately...
  37. W

    Continuous Charge Distribution?

    http://www.vias.org/physics/bk4_06_07.html This is a quote from the mentioned website, " For example, a charged metal ball will have charge spread nearly uniformly all over its surface, and in for most purposes it will make sense to ignore the fact that this uniformity is broken at the atomic...
  38. J

    Finding a C1 Function for Continuous f,g in Real Numbers

    Hello,I need some advice on a problem. Let f,g:R\rightarrow R (where R denotes the real numbers) be two continuous functions, assume that f(x) < g(x) \forall x \neq 0 , and f(0) = g(0).Define A = \left\{(x,y)\neq (0,0): y< f(x),x \in R\right\} B = \left\{(x,y)\neq (0,0): y> g(x),x \in...
  39. W

    Continuous Charge Distribution: Symmetry & Meaning

    In the Electric field of a Continuous Charge Distribution, what is "conti.." exactly? -I know its the "distribution"! but I`m asking about, like, how would the "distribution" be continuous? -I think the word "symmetry" should be used? -why is the word "continuous" used?
  40. M

    How to show continuous at each point in R^2

    Homework Statement f(x , y) = y^3 + x^3 Calculate the partial derivatives fx and fy and show they are continuous at each point (x,y) ∈ R^2 Homework Equations A function is continuous on a region R in the xy-plane if it is continuous at each point in R A function f is continuous at...
  41. P

    PDF of function of 3 continuous, uniform random variables?

    Hi. The question is: Given X, Y and Z are all continuous, independant random variables uniformly distributed on (0,1), prove that (XY)^Z is also uniformly distributed on (0,1). I worked out the pdf of XY=W. I think it's -ln(w). I have no idea at all how to show that W^Z is U(0,1). What...
  42. T

    Proving Continuous Function: Expectation Values of Periodic Functions Over Time

    Hi. I'm looking to at how expectation values of periodic functions evolve in time, and i need to prove that ##\exp ( i \theta )## is continuous in time (this is the expectation of the exponential of the angle). My formula is: ##\exp( i \theta) = \exp ( i t /2) \sum_{n=-\infty}^{\infty} a_n...
  43. wolram

    Longest continuous running lab experiment

    What is the longest continuous running experiment , By continuous i mean some equipment is set up and left to run, not some thing like CERN where there has been periods of down time.
  44. D

    Continuous functions of nxn invertible matrices

    Ok, so this was assigned as a bonus problem in my Topology class a while ago. Nobody in the class got it, but I've still been racking my brain on it ever since. ____ For some n, consider the set of all nxn nonsingular matrices, and using the usual Euclidean topology on this space, show that...
  45. H

    If f is continuous at c and f(c)>1

    Homework Statement Hi everyone, this is probably an easy question but I'm having trouble on the wording of the proof. Let f be continuous at x=c and f(c) > 1 Show that there exists an r > 0 such that \forall x \in B(c,r) \bigcap D : f(x) > 1 Homework Equations \forall \epsilon >...
  46. N

    Most Powerful Continuous Laser

    Hi all, I am trying to find out what is the world's most powerful continuous laser? I would also like to know: - what wavelength range does it operate at and is there a trade-off between bandwidth and max power? - is there a graph anywhere showing laser power as a function of date...
  47. K

    Expectation of a function of a continuous random variable

    If W=g(X) is a function of continuous random variable X, then E(W)=E[g(X)]= ∞ ∫g(x) [fX(x)] dx -∞ ============================ Even though X is continuous, g(X) might not be continuous. If W happens to be a discrete random variable, does the above still hold? Do we still integrate ∫...
  48. B

    Is a graph Continuous and differentiable at a given point

    Homework Statement F f(x)={(2x-1)/Absolute value(2x-1) x cannot equal (1/2) { 0 x = (1/2) a) is f continuous at X = (1/2) explain b) is f differentiable at x = (1/2) explain Homework Equations I have made the graph and x is a point...
  49. K

    Proof about uniformly continuous functions

    Let f be a uniformly continuous function on Q... Prove that there is a continuous function g on R extending f (that is, g(x) = f(x), for all x∈Q I think I am supposed to somehow use the denseness of Q and the continuity of a function to prove this, but I am not quite sure where I should start...
  50. P

    Prob and stats continuous random variable question

    Homework Statement Let X denote the lifetime of a radio, in years, manufactured by a certain company. The density function of X is given by f(x)=\left\{\stackrel{\frac{1}{15}e^\frac{-x}{15}\ \ \ \ if\ 0\ \leq\ x\ <\ \infty}{0\\\\elsewhere} What is the probability that, of eight such...
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