A semidefinite lift of a convex set is an exact representation using linear
equations in a positive semidefinite
matrix followed by an affine function. A lift
of size
has the form
where
is an
real matrix,
is a linear transformation,
is a fixed vector,
and
is an affine function. Here
requires
to be symmetric and positive semidefinite (Fawzi et al.
2015). The interval
has a size-2 lift using the diagonal
matrices
with
.