Function main

examples/extended/dynamics.cpp:130–193

 */

int main() {
    initQuESTEnv();

    // prepare qureg=|0>, H and O
    int numQubits = 20;
    Qureg qureg = createQureg(numQubits);
    PauliStrSum hamil = createMyHamiltonian(numQubits);
    PauliStrSum observ = createMyObservable(numQubits);

    // init qureg=|+> and report qureg, H, O
    initPlusState(qureg);
    reportMyStructs(qureg, hamil, observ);

    // tidy reporting of below expectation values
    setMaxNumReportedSigFigs(3);
    setNumReportedNewlines(1);

    // evolve by repeatedly (each is a "step") Trotterising
    // exp(-i dt H) with the specified order and repetitions.
    qreal dt  = 0.1;
    int order = 4;
    int reps  = 5;
    int steps = 20;

    for (int i=0; i<steps; i++) {

        // evolve qureg under (approx) exp(-i dt H)
        applyTrotterizedUnitaryTimeEvolution(qureg, hamil, dt, order, reps);

        // calculate and report <O>
        qreal time = dt * (i+1);
        qreal expec = calcExpecPauliStrSum(qureg, observ);
        reportScalar("<O(t=" + std::to_string(time) + ")>", expec);
    }

    reportStr("");
    
    // preview the final state...
    setNumReportedNewlines(2);
    setMaxNumReportedItems(25, 25);
    reportStr("[Final state]");
    reportQureg(qureg);

    // and some of its properties...
    reportScalar("Normalisation", calcTotalProb(qureg));
    reportScalar("Probability of first qubit", calcProbOfQubitOutcome(qureg, 0, 0));

    // including the overlap with |+>
    for (int i=0; i<numQubits; i++) 
        applyHadamard(qureg, i);
    reportScalar("Probability of initial state", calcProbOfBasisState(qureg, 0));

    // verify results by uninterrupted higher-order simulation to target time
    initPlusState(qureg);
    applyTrotterizedUnitaryTimeEvolution(qureg, hamil, dt*steps, order+2, reps*steps);
    reportScalar("final <O>", calcExpecPauliStrSum(qureg, observ));

    // clean up