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Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.

1 vote

How is $|J_k u(x)|$ (in the coarea formula) defined when $Du$ does not have full rank?

It is defined through the same formula! For $k \times n$ matrix $Df$, we have $Df \cdot Df^T$ a square $k \times k$ matrix, so its determinant is defined. There is a linear algebra lemma relating it t …
Behnam Esmayli's user avatar
2 votes
3 answers
773 views

A Curved/Warped Version of Fubini's Theorem

I will think of $ \mathbb{R}^{n+m}$ as $\mathbb{R}^n \times \mathbb{R}^m$. Let $ V \subset \mathbb{R}^{n+m}$ be open and $g:V \to U \subset \mathbb{R}^{n+m} $ be a $C^1$ diffeomorphism. For a fixed …
Behnam Esmayli's user avatar
0 votes
Accepted

A Curved/Warped Version of Fubini's Theorem

I have the answer here: Fubini's Theorem on Arbitrary Foliations $$\int_U f = \int_{U_{\eta_0}} \left(\int_{U_\xi} f(\xi,\eta) \frac{|\det DG_{U_\xi} (\xi,\eta)| \cdot |\det DG_{U_{\eta_0}} (\xi,\eta …
Behnam Esmayli's user avatar
6 votes
1 answer
1k views

Fubini's theorem on arbitrary foliations

In what follows $ \mathbb{R}^{n+m} = \{(x,y): x \in \mathbb{R}^n, \ y \in \mathbb{R}^m \} \ .$ Suppose $G: U \to V $ is a $C^1$-diffeomorphism from an open subset of a manifold to an open subset of …
Behnam Esmayli's user avatar