A harmonic polytope is a special type of convex shape. It's the convex hull of a set of vectors that satisfy three key conditions:
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They're on a sphere: All the vectors have a length of 1 and lie on the surface of a
$d$ -dimensional unit sphere. - They're centered: The sum of all the vectors is zero. This means their average position, or centroid, is at the origin.
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They're isotropic: The vectors are perfectly balanced in every direction. This is defined by their empirical covariance matrix, which is a key concept. For a set of
$n$ vectors in$d$ -dimensional space, this matrix is calculated as a sum of outer products of the vectors. The isotropy condition means this matrix is a multiple of the identity matrix. The text proves that this multiple must be exactly 1 divided by$d$ .
In simple terms, a harmonic polytope is the shape you get when you take a bunch of unit vectors that are perfectly balanced and centered, and you form the smallest convex shap