Category:Measures

From ProofWiki
Jump to navigation Jump to search

This category contains results about measures.

Definition 1

$\mu$ is called a measure on $\Sigma$ if and only if $\mu$ fulfils the following axioms:

\((1)\)   $:$     \(\ds \forall E \in \Sigma:\)    \(\ds \map \mu E \)   \(\ds \ge \)   \(\ds 0 \)      
\((2)\)   $:$     \(\ds \forall \sequence {S_n}_{n \mathop \in \N} \subseteq \Sigma: \forall i, j \in \N: S_i \cap S_j = \O:\)    \(\ds \map \mu {\bigcup_{n \mathop = 1}^\infty S_n} \)   \(\ds = \)   \(\ds \sum_{n \mathop = 1}^\infty \map \mu {S_n} \)      that is, $\mu$ is a countably additive function
\((3)\)   $:$     \(\ds \exists E \in \Sigma:\)    \(\ds \map \mu E \)   \(\ds \in \)   \(\ds \R \)      that is, there exists at least one $E \in \Sigma$ such that $\map \mu E$ is finite


Definition 2

$\mu$ is called a measure on $\Sigma$ if and only if $\mu$ fulfils the following axioms:

\((1')\)   $:$     \(\ds \forall E \in \Sigma:\)    \(\ds \map \mu E \)   \(\ds \ge \)   \(\ds 0 \)      
\((2')\)   $:$     \(\ds \forall \sequence {S_n}_{n \mathop \in \N} \subseteq \Sigma: \forall i, j \in \N: S_i \cap S_j = \O:\)    \(\ds \map \mu {\bigcup_{n \mathop = 1}^\infty S_n} \)   \(\ds = \)   \(\ds \sum_{n \mathop = 1}^\infty \map \mu {S_n} \)      that is, $\mu$ is a countably additive function
\((3')\)   $:$      \(\ds \map \mu \O \)   \(\ds = \)   \(\ds 0 \)      

Subcategories

This category has the following 22 subcategories, out of 22 total.