# What is simplicial complexes in algebraic topology?

What is simplicial complexes in algebraic topology?

## What is simplicial complexes in algebraic topology?

In algebraic topology, simplicial complexes are often useful for concrete calculations. For the definition of homology groups of a simplicial complex, one can read the corresponding chain complex directly, provided that consistent orientations are made of all simplices.

Why are simplicial complexes important?

Simplicial complexes were originally used to describe pre-existing topological spaces such as manifolds, as in the question. But now they are the key tool in constructing discrete models for topological spaces.

### How do you create a simplicial complex?

To build one, take the origin and 1 other point which lies on a coordinate axis. This construction, produces two 0-subsimplices. Next, connect the two points to get your 1-simplex σ1 = ⟨p0,p1⟩. 2-simplex (a simplex ⟨p0,p1,p2⟩ generated by three points, p0, p1, p2) A 2-simplex is a solid triangle (including its border).

Is every simplicial complex a CW complex?

Notably the geometric realization of every simplicial set, hence also of every groupoid, 2-groupoid, etc., is a CW complex. Milnor has argued that the category of spaces which are homotopy equivalent to CW-complexes, also called m-cofibrant spaces, is a convenient category of spaces for algebraic topology.

## What does CW complex stand for?

A CW complex is a kind of a topological space that is particularly important in algebraic topology. It was introduced by J. H. C. Whitehead to meet the needs of homotopy theory.

What is a CW pair?

In algebraic topology by a CW-pair (X,A) is meant a CW-complex X equipped with a sub-complex inclusion A↪X.

### Why are Betti numbers important?

In algebraic topology, the Betti numbers are used to distinguish topological spaces based on the connectivity of n-dimensional simplicial complexes.

What is Betti curve?

The Betti curve is a function mapping a persistence diagram to an integer-valued. curve, i.e. each Betti curve is a function B: R → N. Topological Data Analysis for Machine Learning. Bastian Rieck. 14th September 2020 14/30.

## Are simplicial complexes CW-complexes?

simplicial complex. Its n-skeleton Xn ⊂ X is formed by keeping only the i-simplices for i ≤ n. Since there is a homeomorphism (∆n,∂∆n) ∼= (DnSn−1), it is clear that X is a finite cw-complex, with one n-cell for each n-simplex. Despite appearances, simplicial complexes include many spaces of interest.

Is every simplicial complex a CW-complex?

### Is a CW complex a manifold?

Every compact smooth manifold admits a smooth triangulation and hence a CW-complex structure.