# Are continuous functions dense in L infinity?

## Are continuous functions dense in L infinity?

So continuous functions are dense in the step functions, and hence, Lp. f ∈ L∞, but ||f −s||∞ ≥ 1/2 for any step function s.

## Are continuous functions dense in L1?

Continuous functions dense in L1 If X is a complete doubling metric space equipped with a complete probability measure μ such that all Borel sets are μ-measurable, then Cc(X) — the continuous functions with compact support — are dense in L1(μ).

Are step functions dense in L1?

Theorem 2. D = {step functions} is dense in L1. any measurable set A with finite measure, and any ϵ > 0, there exists some g ∈ D such that ∥χA − g∥L1 < ϵ.

### What is an L Infinity function?

L∞ is a function space. Its elements are the essentially bounded measurable functions. More precisely, L∞ is defined based on an underlying measure space, (S, Σ, μ). Start with the set of all measurable functions from S to R which are essentially bounded, i.e. bounded up to a set of measure zero.

### What is the norm of L infinity?

Gives the largest magnitude among each element of a vector. Having the vector X= [-6, 4, 2], the L-infinity norm is 6. In L-infinity norm, only the largest element has any effect.

Are the continuous functions dense in L2?

The set C([0, 1], R) is dense in L2[0, 1]. Proof. Therefore, by the Lebesgue dominated convergence theorem, it follows that f − sn L2 = 0. Thus, since every simple function can be approximated by a continuous function, every nonnegative function can be approximated by a sequence of continuous functions.

## Are LP spaces complete?

[1.3] Theorem: The space Lp(X) is a complete metric space.

## Are simple functions dense in LP?

For general measure spaces, the simple functions are dense in Lp. It is sufficient to prove that we can approximate a positive function f : X → [0, ∞) by simple functions, since a general function may be decomposed into its positive and negative parts.

What is the simplest function?

A basic example of a simple function is the floor function over the half-open interval [1, 9), whose only values are {1, 2, 3, 4, 5, 6, 7, 8}. A more advanced example is the Dirichlet function over the real line, which takes the value 1 if x is rational and 0 otherwise.

### Is Infinity Norm convex?

Infinity norm for a vector is defined by | z ||0o = maxi|z;l. Recall least squares data fitting; in general, minimizing any vector norm of Ax – b is a convex problem. Data fitting in the presence of outliers • If you want a solution robust to outliers: use 11-norm.

### What is L Infinity metric?

Are polynomials dense in L2?

for some λ>0, then the polynomials are dense in L2(R,P).

## Why are continuous functions not dense in L1?

p<\. So continuous functions are dense in the step functions, and hence, Lp. Step functions are not dense in L1: let f= P 1 n=2˜ [1 2n+1; 1 2n . f2L1, but jjf sjj 1\=2 for any step function s. Continuous functions are not dense in L1, because [0;1] is compact, and uniform (L1) limits of uniformly contin- uous functions are continuous.

## Is the space of continuous functions on [ 0, Infinity )?

Consider the vector space of all continuous functions f on [0, infinity), such that the limit lim f (x) when x converges to infinity does exist and is finite. Extend any such function to a continuous function on the compact space [0,infinity] (Alexandroff compactification.) by means of:: f (infinity):= lim f (x) when x converges to infinity.

Is the space of simple functions dense in LP?

This implies that the space of simple functions is also dense in Lp(Rn). In this section we prove that the space of smooth functions with compact supports, and the space of functions with rapidly decreasing derivatives are also dense in L(Rn).

### Is the space C [ 0, Infinity ) complete?

If you consider the space C^b [0,\\infty) of bounded continuous functions (or the space suggested yb Luiz) , then the sup norm is well defined, and this space is complete (basically since the uniform limit of continuous functions is continuous). The space C [a,b] with the sup norm is Banach. However, I am not sure about the space C [0,infinty).

27/04/2021