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From the Cauchy-Schwarz inequality, we can prove that $$\lVert w(x)\rVert^2_{L^2_{[0,1]}}=\int_0^1 w(x)^2\, dx \leq \sqrt{\int_0^1 w(x) \,dx}\cdot \sqrt{\int_0^1 w(x)^3\, dx}.$$

Is it possible to prove another inequality with the other direction, that is, $$\int_0^1 w(x)^3\, dx \leq C_1\cdot \left(\int_0^1 w(x)^2 dx\right)^{1/n}\;?$$

Thanks a lot!!!

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    We have $$\int_0^1 w(x)^3\, dx \leq \max\{w(x)\} \cdot \left(\int_0^1 w(x)^2 dx\right)\;$$ and with some special boundary condition, we can have $\max\{w(x)\}<=c \cdot \|w\|^{1/2} \cdot \|w_x\|^{1/2}$ or $max{w(x)}<=c \cdot \|w_x\|$, but what I want is whether we can get a constant $C_1$ in the above inequality? Thanks.2012-08-16
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    :I already gave you the constant $C$ under certain conditions in my answer.2012-08-16

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