This quantity is calculated after each step in a namesake iterative renormalization group method which divides the system into left and right blocks in order to determine the ground state for one-dimensional systems. The time-evolution of this operator is proportional to its commutator with respect to the Hamiltonian and is expressed as the Liouville equation. The entropy of a system can be determined by examining the trace of this operator multiplied by its own natural 
This quantity is calculated after each step in a namesake iterative renormalization group method which divides the system into left and right blocks in order to determine the ground state for one-dimensional systems. The time-evolution of this operator is proportional to its commutator with respect to the Hamiltonian and is expressed as the Liouville equation. The entropy of a system can be determined by examining the trace of this operator multiplied by its own natural logarithm and expectation values of operators can be computed by taking the trace of the product of this entity and the corresponding operator. This entity is equal to its own square if it represents a pure state, and unlike a wavefunction, this entity can be used to describe mixed states. For 10 points, identify this trace-one, Hermitian matrix which provides an alternate formalism to quantum mechanics and which has a name suggesting it has units of inverse volume.
This quantity is calculated after each step in a namesake iterative renormalization group method which divides the system into left and right blocks in order to determine the ground state for one-dimensional systems.
density matrix or density operator