cleanup: Remove unused features

src/qibo/models/dbi/utils.py

@@ -8,31 +8,6 @@
 from qibo.hamiltonians import SymbolicHamiltonian
 
 
-def commutator(a, b):
-    """Compute commutator between two arrays."""
-    return a @ b - b @ a
-
-
-def variance(a, state):
-    """Calculates the variance of a matrix A with respect to a state:
-    Var($A$) = $\\langle\\mu|A^2|\\mu\rangle-\\langle\\mu|A|\\mu\rangle^2$"""
-    b = a @ a
-    return state.conj().T @ b @ state - (state.conj().T @ a @ state) ** 2
-
-
-def covariance(a, b, state):
-    """This is a generalization of the notion of covariance, needed for the polynomial expansion of the energy fluctuation,
-    applied to two operators A and B with respect to a state:
-    Cov($A,B$) = $\\langle\\mu|AB|\\mu\rangle-\\langle\\mu|A|\\mu\rangle\\langle\\mu|B|\\mu\rangle$
-    """
-
-    c = a @ b + b @ a
-    return (
-        state.conj().T @ c @ state
-        - 2 * state.conj().T @ a @ state * state.conj().T @ b @ state
-    )
-
-
 def generate_Z_operators(nqubits: int, backend=None):
     """Generate a dictionary containing 1) all possible products of Pauli Z operators for L = n_qubits and 2) their respective names.
     Return: Dictionary with operator names (str) as keys and operators (np.array) as values