Homology, boundary maps and the torus computation
Research context
research method · established · As of 2026-10-10
A chain complex has boundary maps with boundary²=0, and homology is cycles modulo boundaries.
Key knowledge
A chain complex has boundary maps with boundary²=0, and homology is cycles modulo boundaries. Singular homology is homotopy invariant; cellular chains compute it for CW complexes. The torus has one zero-cell, two one-cells and one two-cell with zero cellular boundaries, giving H0=Z, H1=Z², H2=Z. These abelian invariants retain less information than all homotopy data.
Values and equations
H_n=ker(partial_n)/im(partial_(n+1)); partial_n partial_(n+1)=0
- partial_n
- Chain boundary map C-n to C-(n-1)
- H_n
- n-th homology group
Conditions and scope
- The displayed torus result uses integer coefficients and the usual CW cell attachment.
- Cell counts alone do not determine homology: attaching maps determine boundary homomorphisms.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §1.1 paths/fundamental group and §2.1 chains, cellular homology pp. 137–141 including surface computations. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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