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world:minkovski [2025/01/29 09:42] rdouc [Proof] |
world:minkovski [2025/01/29 09:44] (current) rdouc [Proof] |
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Using Hölder’s inequality for the second term, we can bound $\varphi'(s)$ as follows: | Using Hölder’s inequality for the second term, we can bound $\varphi'(s)$ as follows: | ||
$$\varphi'(s) \leq \lr{\int (f + s g)^p \rmd \mu}^{\frac{1}{p} - 1} \lr{\int (f + s g)^p \rmd \mu}^{\frac{p-1}{p}} \lr{\int g^p \rmd \mu}^{1/p} = \lr{\int g^p \rmd \mu}^{1/p}.$$ | $$\varphi'(s) \leq \lr{\int (f + s g)^p \rmd \mu}^{\frac{1}{p} - 1} \lr{\int (f + s g)^p \rmd \mu}^{\frac{p-1}{p}} \lr{\int g^p \rmd \mu}^{1/p} = \lr{\int g^p \rmd \mu}^{1/p}.$$ | ||
- | Integrating $\varphi'(s)$ from $0$ to $1$, we obtain $$\lr{\int (f + g)^p \rmd \mu}^{1/p} - \lr{\int f^p \rmd \mu}^{1/p} = \varphi(1) - \varphi(0) = \int_0^1 \varphi'(s) \, \rmd s \leq \lr{\int g^p \rmd \mu}^{1/p}.$$ This completes the proof. | + | Hence, |
+ | $$\lr{\int (f + g)^p \rmd \mu}^{1/p} = \varphi(1) = \varphi(0) + \int_0^1 \varphi'(s) \, \rmd s \leq \lr{\int f^p \rmd \mu}^{1/p}+ \lr{\int g^p \rmd \mu}^{1/p}.$$ This completes the proof. | ||