About the unimprobality of the limiting embedding theorem for different metrics in the Lorentz spaces with Hermite's weight
E. S. Smailova,
A. I. Takuadinab a Institute of Applied Mathematics National Academy of Sciences of Kazakhstan, Karaganda, Kazakhstan
b Karaganda State Medical University, Karaganda, Kazakhstan
Abstract:
In this article we obtained inequality of different metrics in the Lorentz spaces with Hermit's weight for multiple algebraic polynomials. On this basis we established a sufficient condition of embedding of different metrics in the Lorenz spaces with Hermite's weight. Its unimprobality is shown in terms of the “extreme function”.
Let
$f\in L_{p,\theta}(\mathbb R_n;\rho_n)$,
$1\leq p<+\infty$,
$1\leq\theta\leq+\infty$. The sequense
$t\{l_k\}_{k=0}^{+\infty}\subset\mathbb N$ is such that
$l_0=1$ and
$l_{k+1}\cdot l_k^{-1}>a_0>1$,
$\forall k\in\mathbb Z^+$. $f(\bar x)=\sum_{k=0}^{+\infty}\Delta_{l_k,\dots,l_k}(f;\bar x)$ is some presentation of the functions in the metric
$L_{p,\theta}(\mathbb R_n;\rho_n)$, where $\Delta_{l_0,\dots,l_0}(f;\bar x)=T_{1,\dots,1},\Delta_{l_k,\dots,l_k}(f;\bar x)=T_{l_k,\dots,l_k}(\bar x)-T_{l_{k-1},\dots,l_{k-1}}(\bar x)$,
$\forall k\in\mathbb N$. Here
$$
T_{l_k,\dots,l_k}(\bar x)=\sum_{m_1=0}^{l_k-1}\dots\sum_{m_n=0}^{l_k-1}a_{m_1,\dots,m_n}\prod^n_{i=1}x^{m_i}_i
$$
are algebraic polynomials for all
$k\in\mathbb Z^+$.
$1^0$. If the series
$$
A(f)_{p\theta}=\sum_{k=0}^{+\infty}l_k^{\tau(\frac n{2p}-\frac n{2q})}\|\Delta_{l_k,\dots,l_k}(f)\|_{L_{p,\theta}(\mathbb R_n;\rho_n)}^\tau
$$
converge under some
$q$ and
$\tau$:
$p<q<+\infty$,
$0<\tau<+\infty$, then
$f\in L_{q,\tau}(\mathbb R_n;\rho_n)$ and we have the inequality
$$
\|f\|_{L_{q,\tau}(\mathbb R_n;\rho_n)}\leq C_{pq\theta\tau n}\times(A(f)_{p\theta})^\frac1\tau.
$$
$2^0$. The condition
$1^0$ is unimprovable in the sense that there exists a function
$f_0\in L_{p,\theta}(\mathbb R_n;\rho_n)$ and
$A(f_0)_{p\theta}$ diverges for it and
$f_0\notin L_{q,\tau}(\mathbb R_n;\rho_n)$. At the same time, the function $f_0\in L_{q-\varepsilon,\tau}(\mathbb R_n;\rho_n)$ for all
$\varepsilon>0$:
$p<(q-\varepsilon)<q$.
Keywords:
Lorentz's space, Hermitte's weight, nonincreasing rearrangement, inequality of different metrics, theorem in embedding, non improving.
UDC:
517.51 Received: 13.07.2011