What is "spectrahedron"

n. (context mathematics English) The intersection of the cone of positive semidefinite matrix with an affine-linear space

In convex geometry, a spectrahedron is a shape that can be represented as a linear matrix inequality. Alternatively, the set of positive semidefinite matrices forms a convex cone in , and a spectrahedron is a shape that can be formed by intersecting this cone with a linear affine subspace.

Spectrahedra are the solution spaces of semidefinite programs.