# Quick Answer: What Is A Complete Vector Space?

## How do you show a subspace is closed?

A subspace is closed under the operations of the vector space it is in.

In this case, if you add two vectors in the space, it’s sum must be in it.

So if you take any vector in the space, and add it’s negative, it’s sum is the zero vector, which is then by definition in the subspace..

## What does it mean for a space to be complete?

In mathematical analysis, a metric space M is called complete (or a Cauchy space) if every Cauchy sequence of points in M has a limit that is also in M or, alternatively, if every Cauchy sequence in M converges in M. Intuitively, a space is complete if there are no “points missing” from it (inside or at the boundary).

## How do you show a space is complete?

A metric space (X, d) is called complete if every Cauchy sequence (xn) in X converges to some point of X. A subset A of X is called complete if A as a metric subspace of (X, d) is complete, that is, if every Cauchy sequence (xn) in A converges to a point in A.

## What is a real vector space?

A real vector space is a vector space whose field of scalars is the field of reals. A linear transformation between real vector spaces is given by a matrix with real entries (i.e., a real matrix).

## Are the rationals complete?

The real numbers are complete in the sense that every set of reals which is bounded above has a least upper bound and every set bounded below has a greatest lower bound. The rationals do not have this property because there is a “gap” at every irrational number.

## Do all Cauchy sequences converge?

In a complete metric space, every Cauchy sequence is convergent. This is because it is the definition of Complete metric space . … This shows that every Cauchy sequence in converges to a point in , so is a complete metric space.

## Is a complete metric space closed?

A metric space (X, d) is said to be complete if every Cauchy sequence in X converges (to a point in X). Theorem 4. A closed subset of a complete metric space is a complete sub- space. … A complete subspace of a metric space is a closed subset.

## Is the set of integers complete?

The integers, for the metric defined by d(x,y) = |x-y|, are a discrete metric space and thus they are complete since a Cauchy sequence of integers is eventually constant. … Every discrete metric space is complete.

## What is a Cauchy?

In mathematics, a Cauchy sequence (French pronunciation: ​[koʃi]; English: /ˈkoʊʃiː/ KOH-shee), named after Augustin-Louis Cauchy, is a sequence whose elements become arbitrarily close to each other as the sequence progresses.

## Is a metric space open?

Given any metric space, , is both open and closed. Let , then is open if and only if for every there exist such that . This definition is always satisfied for the empty set, , and the entire space, . … In the case of any metric space, the entire space and the empty set fall under “…they [are] both…”