Function calcExpecDiagonalOp

pub unsafe extern "C" fn calcExpecDiagonalOp(
    qureg: Qureg,
    op: DiagonalOp,
) -> Complex

Computes the expected value of the diagonal operator \p op for state \p qureg. Since \p op is not necessarily Hermitian, the expected value may be a complex number.

Let \f$ D \f$ be the diagonal operator \p op, with diagonal elements \f$ d_i \f$. Then if \p qureg is a state-vector \f$|\psi\rangle \f$, this function computes \f[ \langle \psi | D | \psi \rangle = \sum_i |\psi_i|^2 , d_i \f] If \p qureg is a density matrix \f$ \rho \f$, this function computes \f[ \text{Trace}( D \rho ) = \sum_i \rho_{ii} , d_i \f]

@see

• createDiagonalOp()
• applyDiagonalOp()
• calcExpecPauliSum()
• calcExpecPauliProd()
• calcExpecPauliHamil()

@ingroup calc @param[in] qureg a state-vector or density matrix @param[in] op the diagonal operator to compute the expected value of @return the expected vaulue of the operator @throws invalidQuESTInputError()

• if \p op was not created
• if \p op acts on a different number of qubits than \p qureg represents @author Tyson Jones