Reduced homology
In my understanding, the reduced homology is better-behaved than the usual singular homology because the $0$th reduced homology
- counts the non-trivial "closed" $0$-chain and
- reflects the idea of "orientation is the volume form".
(see below for detail)
Poincare duality for singular (co)homologies
On the other hand, the Poincare duality for the usual singular (co)homologies:
$$H_i(X) \cong H^{n-i}(X)$$ holds for an oriented closed manifold $X$.
Question
So I thought there should be a correspondence of the Poincare duality for the reduced homology. That is, let $\tilde{H}'_\bullet, \tilde{H}^\bullet$ be reduced homology and the "reduced cohomology" thing (I don't know what's this). Then,
$$\tilde{H}_i(X) \cong \tilde{H}^{n-i}(X)$$ holds for an oriented closed manifold $X$.
Is there anything like this?
I Googled and found a "reduced cohomology" but found nothing about the duality between them similar to the Poincare duality.
Two reasons why I think the reduced homology is better-behaved than the usual one;
-
we can regard "closed" $0$-chain as the one whose weight is $0$. So it matches well to the idea "n-th homology count the number of nontrivial(non null-homologous) closed n-chain" at $n=0$.
-
By definition of n-simplex ($n\geq 0$), we think them as n-triangle with orientation but without orientation when $n=0$. This is odd. The orientation is (an equivalence class of) the volume form, so the orientation of $0$-triangle should be the scalar field on the $0$-triangle. This naturally leads to the definition of reduced homology.
Any reference would be appreciated.
Thanks in advance.
Best Answer
No. We have $\tilde H_k(X) = H_k(X)$ for $k > 0$ and $\tilde H_0(X) \oplus \mathbb Z \approx H_0(X)$, similarly for cohomology. Thus
$$\tilde H_i(X) \approx \tilde H^{n-i}(X)$$ for all $i$ with $0 < i < n$. For $i = 0, n$ it is wrong.