SkVectorNorm

SkVectorNorm is a function that computes the s(k)-norm of a vector (i.e., the Euclidean norm of the vector of its k largest Schmidt coefficients ).

Syntax

 * SkVectorNorm(VEC)
 * SkVectorNorm(VEC,K)
 * SkVectorNorm(VEC,K,DIM)

Argument descriptions

 * VEC: A vector living in bipartite space.
 * K (optional, default 1): A positive integer.
 * DIM (optional, by default has both subsystems of equal dimension): A 1-by-2 vector containing the dimensions of the subsystems that VEC lives on.

Sum of squares of eigenvalues of reduced density matrix
The square of the s(k)-vector norm is equal to the Ky Fan k-norm of the vector's reduced density matrix: