The Schatten -norm
of an
complex matrix
is the vector norm of its singular values. If
and the singular values
are
, then for
,
while
The Schatten 1-norm is the sum of the singular values, the Schatten 2-norm is the Frobenius norm or Hilbert-Schmidt norm, and the Schatten infinity-norm is the spectral norm. Multiplication on either side by a unitary matrix leaves a Schatten norm unchanged.
The Schatten class
consists of compact operators on a Hilbert
space whose singular values have finite
-norm. Long (2026) reported that the
Hilbert transform on
has sharp operator norm
, where
and
.