Function rand_getRandomMultiQubitOutcome

quest/src/core/randomiser.cpp:140–166

qindex rand_getRandomMultiQubitOutcome(vector<qreal> probs) {

    // assumes sum(probs) = 1, and produces a multinomial variate
    // which is always consistent between distributed nodes

    std::uniform_real_distribution<qreal> distrib(0, 1); // ~[0,1]

    // advances generator on every node, retaining consensus
    qreal sample = distrib(mainGenerator);

    // map sample to an element of probs
    qreal cumProb = 0;
    for (size_t i=0; i<probs.size(); i++) {
        cumProb += probs[i];

        if (sample < cumProb)
            return i;
    }

    // it is principally possible that cumProb == 1 - eps, and that
    // sample lies within [1-eps, 1], and should take final elem
    if (1 - cumProb <= validateconfig_getEpsilon())
        return probs.size() - 1;

    error_randomiserGivenNonNormalisedProbList();
    return probs.size();
}