Skip to main content
added 4 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments:

  1. It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  2. The desired result is true once $f$ isfor $C^{n+1}$$f \in C^n (\Omega)$ by Sard's theorem.

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments:

  1. It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  2. The desired result is true once $f$ is $C^{n+1}$ by Sard's theorem.

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments:

  1. It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  2. The desired result is true for $f \in C^n (\Omega)$ by Sard's theorem.

added 80 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments: It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  1. It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  2. The desired result is true once $f$ is $C^{n+1}$ by Sard's theorem.

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments: It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments:

  1. It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

  2. The desired result is true once $f$ is $C^{n+1}$ by Sard's theorem.

added 39 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments: It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments: It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$.

Note: Here $\mathcal H^k$ denotes the $k$-dimensional Hausdorff measure.

Let $f \in C^1 (\mathbb \Omega)$ for some open, connected, bounded subset $\Omega$ of $\mathbb R^n$. We consider for each $t \in \mathbb R$ the level set $E_t := \{x \in \Omega \, | \, f(x) = t\}$.

Question: Is it true that for Lebesgue almost every $t \in \mathbb R$, we have $Df(x) \neq 0$ for $\mathcal H^{n-1}$-almost every $x \in E_t$?

Comments: It is interesting to contrast the desired result to the fact that we have $Df = 0$, $\mathcal H^n$-a.e. on every level set $E_t$. Note that this is not a contradiction!

deleted 9 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99
Loading
edited title
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99
Loading
added 3 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99
Loading
added 148 characters in body
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99
Loading
Source Link
Nate River
  • 6.2k
  • 2
  • 23
  • 99
Loading