Function calcExpecFullStateDiagMatr

quest/src/api/calculations.cpp:161–182

qreal calcExpecFullStateDiagMatr(Qureg qureg, FullStateDiagMatr matrix) {
    validate_quregFields(qureg, __func__);
    validate_matrixFields(matrix, __func__);
    validate_matrixAndQuregAreCompatible(matrix, qureg, true, __func__);
    validate_matrixIsHermitian(matrix, __func__);

    // unused parameters; see calcExpecFullStateDiagMatrPower() for explanation
    qcomp exponent = qcomp(1,0);
    bool useRealPow = false;

    qcomp value = (qureg.isDensityMatrix)?
        localiser_densmatr_calcExpecFullStateDiagMatr(qureg, matrix, exponent, useRealPow):
        localiser_statevec_calcExpecFullStateDiagMatr(qureg, matrix, exponent, useRealPow);

    // the sub-epsilon imaginary components in matrix never damage the real
    // component of the statevector expectation value, so we do not validate
    // imag(value)~0; we can always safely discard it, and only validate for densmatr:
    if (qureg.isDensityMatrix)
        validate_densMatrExpecDiagMatrValueIsReal(value, exponent, __func__);

    return std::real(value);
}


qreal calcExpecFullStateDiagMatrPower(Qureg qureg, FullStateDiagMatr matrix, qreal exponent) {