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Free Fisher Information


Free Fisher information of a self-adjoint tuple X=(X_1,...,X_n) in a von Neumann algebra with a faithful normal tracial state tau is

 Phi^*(X)=sum_(j=1)^n||xi_j||_2^2,

where vectors xi_j satisfy

 tau(xi_jP(X))=(tau tensor tau)((partial_jP)(X))

for every noncommutative polynomial P. Here ||a||_2^2=tau(a^*a), and partial_j is the derivation determined by partial_jx_i=delta_(ij)1 tensor 1 and the product rule. These vectors lie in the L^2 completion of the algebra generated by the tuple. When they do not exist, Phi^*(X)=infty. Integrating this quantity along addition of freely independent semicircular noise defines nonmicrostates free entropy.


See also

Free Entropy, Free Entropy Equality Problem, Free Independence, Semicircular Distribution, Tracial State

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References

Voiculescu, D. "Free Entropy." Bull. London Math. Soc. 34, 257-278, 2002. https://doi.org/10.1112/S0024609301008992.

Cite this as:

Weisstein, Eric W. "Free Fisher Information." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/FreeFisherInformation.html

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