Morrey spaces

Let $1\leq p <\infty$ and $0<\lambda<n$. The set of locally integrable functions $f$ such that $$ \sup_{r>0, x \in \R^n} \dfrac{1}{r^\lambda} \int_{B_r(x)} |f(y)|^p dy <+\infty $$ is called the Morrey space $L^{p,\lambda}(\R^n)$. Different values of $\lambda$ give rise to trivial situations. It is a Banach space (Hilbert if $p=2$) under the norm $$ \|f\|_{p,\lambda} \equiv \sup_{r>0, x \in \R^n} \left(\dfrac{1}{r^\lambda} \int_{B_r(x)} |f(y)|^p dy\right)^{1/p} $$

Morrey spaces were introduced by C.B.Morrey in 1938 in connection with the study of regularity for systems of partial differential equations.

Many operator from Harmonic Analysis are bounded on Morrey spaces. We recall the Maximal operator and the Singular integral operators.