Are all functions continuous?


Are all functions continuous?

Theorem (classically equivalent form): All functions are continuous. When constructive mathematicians says that “all functions are continuous” they have something even better in mind.2006-03-27

Are all functions are continuous?

Theorem: There are no discontinuous functions. Theorem (classically equivalent form): All functions are continuous. When constructive mathematicians says that “all functions are continuous” they have something even better in mind.2006-03-27

How do you know if a function is continuous?

For a function to be continuous at a point, it must be defined at that point, its limit must exist at the point, and the value of the function at that point must equal the value of the limit at that point. Discontinuities may be classified as removable, jump, or infinite.

Which types of functions are continuous?

Exponential functions are continuous at all real numbers. The functions sin x and cos x are continuous at all real numbers. The functions tan x, cosec x, sec x, and cot x are continuous on their respective domains. The functions like log x, ln x, √x, etc are continuous on their respective domains.

What is a real life example of a continuous function?

Suppose you want to use a digital recording device to record yourself singing in the shower. The song comes out as a continuous function.

At which point function is not continuous?

If a function is not continuous at some point, then it is not necessary the given point is not in the domain of the function. This is one reason for discontinuity that any point is not in the domain of the function and the point lies within the boundaries of the function. Example: ln x is discontinuous at x = 0.

Is a continuous function always continuous?

There are several different definitions of (global) continuity of a function, which depend on the nature of its domain. (the whole real line) is often called simply a continuous function; one says also that such a function is continuous everywhere. For example, all polynomial functions are continuous everywhere.

What are not continuous?

Definition of noncontinuous : not continuous: such as. a : having one or more interruptions in a sequence or in a stretch of time or space a noncontinuous hiking trail.

What is continuous function example?

A continuous function is said to be a piecewise continuous function if it is defined differently in different intervals. For example, g(x)={(x+4)3 if x<−28 if x≥−2 g ( x ) = { ( x + 4 ) 3 if x < − 2 8 if x ≥ − 2 is a piecewise continuous function.

Is a function continuous or discontinuous?

continuous function

Can a limit exist but not be continuous?

In short, the limit does not exist if there is a lack of continuity in the neighbourhood about the value of interest. Recall that there doesn’t need to be continuity at the value of interest, just the neighbourhood is required.

What types of functions are continuous on their domains?

g) The cotangent, cosecant, secant and tangent functions are continuous over their domain.

Can a function exist and not be continuous?

Definition. A function is said to be continuous on the interval [a,b] if it is continuous at each point in the interval. Note that this definition is also implicitly assuming that both f(a) and limx→af(x) lim x → a ⁡ exist. If either of these do not exist the function will not be continuous at x=a .2018-05-29

What type of functions are not continuous?

The function value and the limit aren’t the same and so the function is not continuous at this point. This kind of discontinuity in a graph is called a jump discontinuity.2018-05-29

Does a function have to be continuous?

It’s the other way around: a function must be defined at a point x in order to look whether it’s continuous at x. “Point of discontinuity” has very little to do with continuity of the function. For an example, the floor function is defined in x=1, say, but not continuous at that particular point.2013-06-16

Which functions are continuous everywhere?

Rational functions are continuous everywhere in its domain.

Does the function have to be continuous to have a limit?

No, a function can be discontinuous and have a limit. The limit is precisely the continuation that can make it continuous. Let f(x)=1 for x=0,f(x)=0 for x≠0.2015-12-24

Can a function exist if it is discontinuous?

When a function is not continuous at a point, then we can say it is discontinuous at that point. There are several types of behaviors that lead to discontinuities. A removable discontinuity exists when the limit of the function exists, but one or both of the other two conditions is not met.

Does one function have to be continuous?

In other words, a function is continuous if its graph has no holes or breaks in it. For many functions it’s easy to determine where it won’t be continuous. Functions won’t be continuous where we have things like division by zero or logarithms of zero.2018-05-29

Continuous function – Wikipedia

A real function, that is a function from real numbers to real numbers, can be represented by a graph in the Cartesian plane; such a function is continuous if, roughly speaking, the graph is a single unbroken curve whose domain is the entire real line. A more mathematically rigorous definition is given below. Continuity of real functions is usually defined in terms of limits.

Continuous Function – Definition, Graph and Examples

In mathematics, a continuous function is a function that does not have discontinuities that means any unexpected changes in value. A function is continuous if we can ensure arbitrarily small changes by restricting enough minor changes in its input. If the given function is not continuous, then it is said to be discontinuous.

Continuous Functions

Continuous Functions A function is continuous when its graph is a single unbroken curve that you could draw without lifting your pen from the paper. That is not a formal definition, but it helps you understand the idea. Here is a continuous function: Examples So what is not continuous (also called discontinuous) ?

Continuous Function – Definition, Examples, Graph

A continuous function, as its name suggests, is a function whose graph is continuous without any breaks or jumps. i.e., if we are able to draw the curve (graph) of a function without even lifting the pencil, then we say that the function is continuous.

Continuous Functions | Brilliant Math & Science Wiki

In calculus, a continuous function is a real-valued function whose graph does not have any breaks or holes. Continuity lays the foundational groundwork for the intermediate value theorem and extreme value theorem.

Continuous Function — from Wolfram MathWorld

A continuous function can be formally defined as a function where the pre-image of every open set in is open in . More concretely, a function in a single variable is said to be continuous at point if 1. is defined, so that is in the domain of . 2. exists for in the domain of . 3. , where lim denotes a limit .

Continuous Functions: Definition, Examples, and Properties

What is a Continuous Function? A function is continuous everywhere if you can trace its curve on a graph without lifting your pencil. A function is discontinuous at a point if you cannot trace its curve without lifting your pencil at that point; meaning it has a hole, break, jump, or vertical asymptote at that point. For example, the function

Algebra of Continuous Functions

Division of Continuous Function. Theorem: Suppose, f and g are two real functions that are continuous at a point ‘a’, where ‘a’ is a real number. Then the division of the two functions f and g will remain continuous at ‘a’. f (x) ÷ g (x) is continuous at x = a. Proof: Given, lim x→a f (x) = f (a) lim x→ a g (x) = g (a)

READ  Are MOFs polymers?

PDF Continuous Functions – University of California, Berkeley

Continuous Functions Definition: Continuity at a Point A function f is continuous at a point x 0 if lim x→x 0 f(x) = f(x 0) If a function is not continuous at x 0, we say it is discontinuous at x 0. From the above definition, we can see that in order for a function f to be continuous at a point x 0, f must be defined at x 0, and the limit

Function Continuity Calculator – Symbolab

Free function continuity calculator – find whether a function is continuous step-by-step This website uses cookies to ensure you get the best experience. By using this website, you agree to our Cookie Policy.

Continuous function – Conditions, Discontinuities, and

Continuous functions are functions that have no restrictions throughout their domain or a given interval. Their graphs won’t contain any asymptotes or signs of discontinuities as well. The graph of f ( x) = x 3 – 4 x 2 – x + 10 as shown below is a great example of a continuous function’s graph.

A Gentle Introduction to Continuous Functions

Continuous functions are very important in the study of optimization problems. We can see that the extreme value theorem guarantees that within an interval, there will always be a point where the function has a maximum value. The same can be said for a minimum value.

What is a continuous function? – University of Georgia

In other words, a function f is continuous at a point x=a, when (i) the function f is defined at a , (ii) the limit of f as x approaches a from the right-hand and left-hand limits exist and are equal, and (iii) the limit of f as x approaches a is equal to f (a). Before we go further, let’s begin by constructing functions that are not continuous.

Continuous Function / Check the Continuity of a Function

In layman’s terms, a continuous function is one that you can draw without taking your pencil from the paper. If you have holes, jumps, or vertical asymptotes, you will have to lift your pencil up and so do not have a continuous function. If your function jumps like this, it isn’t continuous.

Continuous functions – An approach to calculus

A continuous function The definition of “a function is continuous at a value of x” Limits of continuous functions Removable discontinuity CONTINUOUS MOTION is motion that continues without a break. Its prototype is a straight line. There is no limit to the smallness of the distances traversed.

Continuous function – Encyclopedia of Mathematics

A function , , is called continuous at a point in, say, the variable if the restriction of to the set is continuous at , that is, if the function of the single variable is continuous at . A function , , , can be continuous at in every variable , but need not be continuous at this point jointly in the variables.

1.5: Properties of Continuous Functions – Mathematics

Continuous functions have two important properties that will play key roles in our discussions in the rest of the text: the extreme-value property and the intermediate-value property. Both of these properties rely on technical aspects of the real numbers which lie beyond the scope of this text, and so we will not attempt justifications.

Differentiable vs. Continuous Functions | Rules, Examples

What is a continuous function? A continuous function is a graph of a function that has no breaks and continues on. A formal definition of a continuous function is if {eq}f (x) {/eq} is considered

Continuous Function | Removable, essential, and jump

A function is continuous on an open interval if and only if it is continuous at every number in that open interval. Right-Hand Continuity A function ‘f’ is continuous from the right at the number ‘a’ if and only if the following three conditions get satisfied: f (a) exists.

Continuous Function – an overview | ScienceDirect Topics

The concept of a continuous function is that it is a function, whose graph has no break. For this reason, continuous functions are chosen, as far as possible, to model the real world problems. If a function is such that its limiting value at a point equals the functional value at that point, then we say that the function is continuous there.

How to Determine Whether a Function Is Continuous or

A graph for a function that’s smooth without any holes, jumps, or asymptotes is called continuous. Your pre-calculus teacher will tell you that three things have to be true for a function to be continuous at some value c in its domain: . f(c) must be defined. The function must exist at an x value (c), which means you can’t have a hole in the function (such as a 0 in the denominator).

Continuous uniform distribution – Wikipedia

Definitions Probability density function. The probability density function of the continuous uniform distribution is: = { , < >The values of f(x) at the two boundaries a and b are usually unimportant because they do not alter the values of the integrals of f(x) dx over any interval, nor of x f(x) dx or any higher moment. Sometimes they are chosen to be zero, and sometimes chosen to be 1 / b − a.

Continuous Function: Definition, Graph & Solved Examples

Continuous function is a function in mathematics that is continuous and does not have any discontinuities in its expected range of values. Continuous functions are a very important concept in the understanding of calculus. Moreover, a continuous function is applied in almost every function to ensure small changes in their values.

Calculus I – Continuity – Lamar University

The function value and the limit aren’t the same and so the function is not continuous at this point. This kind of discontinuity in a graph is called a jump discontinuity . Jump discontinuities occur where the graph has a break in it as this graph does and the values of the function to either side of the break are finite ( i.e. the function

2.3: Limits and Continuous Functions – Mathematics LibreTexts

(ii) The exponential function is continuous on the entire plane. Reason: [e^z = e^{x + iy} = e^x cos (y) + ie^x sin (y). nonumber] So the both the real and imaginary parts are clearly continuous as a function of ((x, y)). (iii) The principal branch (text{Arg} (z)) is continuous on the plane minus the non-positive real axis.

Continuous Functions Theorems – Video & Lesson Transcript

Continuous functions. A continuous function in mathematics is defined as a function that is defined at each point in its domain. Basically, a function whose graph is an unbroken curve in its

Continuity of Functions – Math24

Continuity of Elementary Functions. All elementary functions are continuous at any point where they are defined. An elementary function is a function built from a finite number of compositions and combinations using the four operations (addition, subtraction, multiplication, and division) over basic elementary functions.

PDF 6 | Continuous Functions – Buffalo

6 | Continuous Functions Let X, Y be topological spaces. Recall that a function f: X →Y is continuous if for every open set U ⊆Y the set f−1(U) ⊆X is open. In this chapter we study some properties of continuous functions. We also introduce the notion of a homeomorphism that plays a central role in topology: from the topological perspective interesting properties of spaces are the

continuous function | mathematics | Britannica

Continuous functions on a compact set have the important properties of possessing maximum and minimum values and being approximated to any desired precision by properly chosen polynomial series, Fourier series, or various other classes of functions as described by the Stone-Weierstrass approximation theorem. Read More.

CC Continuous Functions – University of Nebraska-Lincoln

A function f f is continuous at x = c x = c provided that. f f has a limit as x → c, x → c, f f is defined at x= c, x = c, and. limx→cf(x) =f(c). lim x → c f ( x) = f ( c). Conditions (a) and (b) are technically contained implicitly in (c), but we state them explicitly to emphasize their individual importance.

READ  Are petite sizes smaller or just shorter?

8.5: Continuous Functions – Mathematics LibreTexts

A continuous function f: X → Y for metric spaces (X, dX) and (Y, dY) is said to be proper if for every compact set K ⊂ Y, the set f − 1(K) is compact. Suppose that a continuous f: (0, 1) → (0, 1) is proper and {xn} is a sequence in (0, 1) that converges to 0. Show that {f(xn)} has no subsequence that converges in (0, 1).

Continuous functions – Free Math Worksheets

The concept of continuity of a function is intuitively clear, however, very complex. Less formal, if the domain of the function is an interval, then the graph of the function we can draw without lifting the pencil from the paper.

Continuous function – Wikipedia

A real function, that is a function from real numbers to real numbers, can be represented by a graph in the Cartesian plane; such a function is continuous if, roughly speaking, the graph is a single unbroken curve whose domain is the entire real line. A more mathematically rigorous definition is given below. A rigorous definition of continuity of real functions is usually given in a first

Continuous Functions: Intuition and How This Concept Is

The concept of continuous functions appears everywhere. All of calculus is about them. In fact, calculus was born because there was a need to describe and study two things that we consider “continuous”: change and motion. In calculus, something being continuous has the same meaning as in everyday use. For example, the growth of a plant is

PDF Lecture 5 : Continuous Functions De nition 1 f a f x f a x

Lecture 5 : Continuous Functions De nition 1 We say the function fis continuous at a number aif lim x!a f(x) = f(a): (i.e. we can make the value of f(x) as close as we like to f(a) by taking xsu ciently close to a). Example Last day we saw that if f(x) is a polynomial, then fis continuous at afor any real number asince lim x!af(x) = f(a).

What is a non constant continuous function

Function f is continuous at a point a if the following conditions are satisfied. Example 1: Show that function f defined below is not continuous at x = – 2. f (-2) is undefined (division by 0 not allowed) therefore function f is discontinuous at x = – 2. Example 2: Show that function f is continuous for all values of x in R.

PDF Continuity – University of Connecticut

functions, we wind up with continuous functions. Again, the exception is if there’s an obvious reason why the new function wouldn’t be con-tinuous somewhere. • The sum of continuous functions is a continuous function. • The difference of continuous functions is a continuous function.

Discontinuous Function – Meaning, Types, Examples

A function in algebra is said to be a discontinuous function if it is not a continuous function. Just like a continuous function has a continuous curve, a discontinuous function has a discontinuous curve. In other words, we can say that the graph of a discontinuous function cannot be made with a single stroke of the pen, i.e., once we put the

Function Continuity, Properties of continuous functions

Definition. A function f (x) is said to be continuous at a point c if the following conditions are satisfied. – f (c) is defined. -lim x → c f (x) exist. -lim x → c f (x) = f (c) – If f (x) is continuous at all points in an interval (a, b), then f (x) is continuous on (a, b) – A function continuous on the interval (-∞; +∞) is called a

Continuous and Discontinuous Functions – Desmos

Continuous and Discontinuous Functions. Log InorSign Up. Continuous Functions. 1. Continuous on their Domain. 11. Discontinuous Functions 15. y = 1 x 16. y = cscx. 17. y = tanx. 18. y = secx. 19. y = cotx. 20. Piecewise. 21. 25. powered by. powered by “x” x “y” y “a” squared a 2 “a” Superscript, “b

Continuity of a Function – Calculus Know-It-ALL

All single-variable, real-number quadratic functions are continuous. The general form of a quadratic function Q is. Q (x )= ax2 + bx + c. where x is the independent variable, a is a nonzero real, and b and c can be any reals. In rect-angular coordinates, the graph of a quadratic function is always a parabola that opens either straight up or

Continuous function Definition & Meaning | Dictionary.com

Continuous function definition, (loosely) a mathematical function such that a small change in the independent variable, or point of the domain, produces only a small change in the value of the function. See more.

PDF Continuous functions and open sets – University of Notre Dame

A function f: U!Rm is continuous (at all points in U) if and only if for each open V ˆRm, the preimage f 1(V) is also open. Proof. Suppose that f is continuous on U and that V ˆRm is open. Given a point a2 f 1(V), we have (by de nition of f 1(V)) that f(a) 2V. Since V is open, there exists >0 such that B(f(a); ) ˆV.

What is a continuous function? + Example – Socratic.org

A continuous function is a function that is continuous at every point in its domain. That is f:A->B is continuous if AA a in A, lim_(x->a) f(x) = f(a) We normally describe a continuous function as one whose graph can be drawn without any jumps. That’s a good place to start, but is misleading. An example of a well behaved continuous function would be f(x) = x^3-x graph{x^3-x [-2.5, 2.5, -1.25

PDF Piecewise Continuous Functions – Dartmouth College

The function f(x) = x2 is continuous at x = 0 by this definition. It is also continuous at every other point on the real line by this definition. If a function is continuous at every point in its domain, we call it a continuous function. The following functions are all continuous: 1 †

Continuous functions, space of – Encyclopedia of Mathematics

A normed space of bounded continuous functions on a topological space with the norm .Convergence of a sequence in means uniform convergence. The space is a commutative Banach algebra with a unit element. If is compact, then every continuous function is bounded, consequently, is the space of all continuous functions on .. When is a closed interval of real numbers, is denoted by .

Continuous Functions – Problem 3 – Calculus Video by

For functions that are not polynomials, before applying the rules of continuous functions (sums, products, quotients, and compositions of continuous functions are also continuous), you must check where the function is defined, and if the function is continuous at each point where it is defined.

measure theory – $f$ a real, continuous function, is it

The answer here shows A contains all open sets; so, by a standard theorem, it contains all Borel sets. It is not true, in general, that the inverse image of a Lebesgue measurable (but not Borel) set under a continuous function must be Lebesgue measurable. The definition of a measurable function in general is that the preimage of every Borel set

Continuous Functions in Calculus

This function is also discontinuous. Taking into consideration all the information gathered from the examples of continuous and discontinuous functions shown above, we define a continuous functions as follows: Function f is continuous at a point a if the following conditions are satisfied.

PDF Math 341 Lecture #22 x4.4: Continuous Functions on Compact

x4.4: Continuous Functions on Compact Sets The Extreme Value Theorem. The topological terms of open, closed, bounded, compact, perfect, and connected are all used to describe subsets of R. A function f: A!R maps a subset Aof R to a subset f(A) of R.

READ  Are there tiger mosquitoes in Florida?

PDF Section 18. Continuous Functions

Continuous Functions 1 Section 18. Continuous Functions Note. Continuity is the fundamental concept in topology! When you hear that “a coffee cup and a doughnut are topologically equivalent,” this is really a claim about the existence of a certain continuous function (this idea is explored in depth

calculus – How to prove that a function is continuous

One property of continuous function is that it has relation with differentiability. Every differentiable function f: ( a, b) → R is continuous. Although the converse does not hold, we can still use this property to prove that a function is continuous. Show activity on this post. lim h → 0 f ( a + h) = f ( a).

ring of continuous functions – PlanetMath

Since taking the absolute value of a continuous function is again continuous, C ⁢ (X) is a sublattice of ℝ X. As a result, we may consider C ⁢ (X) as a lattice-ordered ring of continuous functions.

PDF 1 The space of continuous functions – University of Pittsburgh

of continuous functions from some subset Aof a metric space M to some normed vector space N:The text gives a careful de-nition, calling the space C(A;N). The simplest case is when M= R(= R 1 ).

Continuous Functions.docx – Continuous Functions A

Continuous Functions A function is continuous when its graph is a single unbroken curve .. that you could draw without lifting your pen from the paper. That is not a formal definition, but it helps you understand the idea. Here is a continuous function: Examples So what is not continuous (also called discontinuous) ? Look out for holes, jumps or vertical asymptotes (where the function

continuous function | Example sentences

Examples of how to use “continuous function” in a sentence from the Cambridge Dictionary Labs

MathCS.org – Real Analysis: 6.2. Continuous Functions

Examples 6.2.6: Every polynomial is continuous in R, and every rational function r (x) = p (x) / q (x) is continuous whenever q (x) # 0. The absolute value of any continuous function is continuous. Continuity is defined at a single point, and the epsilon and delta appearing in the definition may be different from one point of continuity to

Algebra of Continuous Functions: Introduction, Rules

Answer: When a function is continuous in nature within its domain, then it is a continuous function. For instance, g(x) does not contain the value ‘x = 1’, so it is continuous in nature. Question 5: Are all continuous functions differentiable? Answer: Any differentiable function can be continuous at all points in its domain. For instance, a

Differentiable Function | Brilliant Math & Science Wiki

In calculus, a differentiable function is a continuous function whose derivative exists at all points on its domain. That is, the graph of a differentiable function must have a (non-vertical) tangent line at each point in its domain, be relatively “smooth” (but not necessarily mathematically smooth), and cannot contain any breaks, corners, or cusps.

Draw a function as a continuous curve — geom_function

Source: R/geom-function.R, R/stat-function.r. geom_function.Rd. Computes and draws a function as a continuous curve. This makes it easy to superimpose a function on top of an existing plot. The function is called with a grid of evenly spaced values along the x axis, and the results are drawn (by default) with a line.

Right-Continuous Function – an overview | ScienceDirect Topics

We call a function f, a continuous function at the point t = t0 if. lim t → t0 f(t) = f(t 0) regardless of the direction t approaches t0. A right-continuous function at t0 has a limiting value only when t approaches t0 from the right direction, i.e. t is larger than t0 in the vicinity of t0. We will denote this as.

Continuity of Functions of One Variable

The following problems involve the CONTINUITY OF A FUNCTION OF ONE VARIABLE. Function y = f(x) is continuous at point x=a if the following three conditions are satisfied : . i.) f(a) is defined , ii.) exists (i.e., is finite) , and iii.) . Function f is said to be continuous on an interval I if f is continuous at each point x in I.Here is a list of some well-known facts related to continuity :

Uniformly Continuous — from Wolfram MathWorld

A map from a metric space to a metric space is said to be uniformly continuous if for every , there exists a such that whenever satisfy .. Note that the here depends on and on but that it is entirely independent of the points and .In this way, uniform continuity is stronger than continuity and so it follows immediately that every uniformly continuous function is continuous.

Continuous Functions – Problem 1 – Calculus Video by

If two functions f, and g are continuous functions, and c is a constant. Then two things; first f (x) plus g (x) will be a continuous function. The constant c times f (x) will also be continuous. So these functions will be continuous wherever they are defined. Let’s take a look at the problem. Explain why the polynomial p (x) equals 3x² minus

PDF Continuous, Nowhere Differentiable Functions

function (originally de ned as a Fourier series) was the rst instance in which the idea that a continuous function must be di erentiable almost everywhere was seriously challenged. Di erentiability, what intuitively seems the default for continuous functions, is in fact a rarity.

Non Continuous Function Examples – calculus is this a

Non Continuous Function Examples. Here are a number of highest rated Non Continuous Function Examples pictures upon internet. We identified it from honorable source. Its submitted by admin in the best field. We endure this nice of Non Continuous Function Examples graphic could possibly be the most

Compact Sets and Continuous Functions

Definition 2:The function f is said to be continuous at if On the other hand, in a first topology course, one might define: Definition 3: A topological space is a pair (X, ) where X is a set and is a collection of subsets of X (called the open sets of the topological space) such that

Fetal in vivo continuous cardiovascular function during

Progress in this field has been hampered in part by the inability to record continuous cardiovascular function in the fetus, including measurement of regional blood flow, as the chronic fetal hypoxia is actually occurring.

Continuous functions form a vector space – Calculus

The continuous functions on form a real vector space, in the sense that the following hold: Additive closure: A sum of continuous functions is continuous: If are both continuous functions on , so is . Scalar multiples: If and is a continuous function on , then is also a continuous function on .

Piecewise Function: Definition, How to Draw – Calculus How To

A piecewise continuous function f(x), defined on the interval (a < x < b), is continuous at any point x in that interval, except that it could be discontinuous for some finite points x i (i = 1, 2, 3…) such that a < x i < b. In addition, both of the following limits exist and are finite (Doshi, 1998):

Is one over x a continuous function? – Quora

Answer (1 of 3): Well, if you open up your calculus textbook, you will see that a function is called continuous if it is continuous at every point of its domain. The domain of f(x)=1/x is all nonzero x. And 1/x is continuous whenever x is nonzero. So yes, f(x)=1/x is a continuous function. Now, e

Continuous Function: study guides and answers on Quizlet

The continuous function f is known to be increasing for all x. Selected values of f are given in the table above. Let L be the left Riemann sum approximation for ∫101f(x)ⅆx using the four subintervals indicated by the table.

Answered: Let f be a uniformly continuous… | bartleby

Let f be a uniformly continuous function