Function mixDensityMatrixWithStatevector

quest/src/core/localiser.cpp:1408–1436

void mixDensityMatrixWithStatevector(qreal outProb, Qureg out, qreal inProb, Qureg in) {

    // we can handle 3 out of 4 possible combinations of distribution,
    // and accelerator.hpp will handle every combination of GPU-accel
    bool outDist = out.isDistributed;
    bool inDist = in.isDistributed;

    // illegal to distribute only the smaller Qureg; 'out' has no buffer space to receive it.
    // in theory, we could allocate a temporary receive buffer since it is merely quadratically
    // smaller than 'out' so will be a negligible memory overhead; but this scenario (having a
    // smaller distributed Qureg) is completely ludicrous and unworth supporting
    if (!outDist && inDist)
        error_mixQuregsAreLocalDensMatrAndDistribStatevec();

    // both non-distributed is trivial
    if (!outDist && !inDist)
        accel_densmatr_mixQureg_subB(outProb, out, inProb, in);

    // both distributed requires broadcasting 'in' into every node's 'out' buffer
    if (outDist && inDist) {
        comm_combineAmpsIntoBuffer(out, in); // uses same buffer that subC() consults
        accel_densmatr_mixQureg_subC(outProb, out, inProb);
    }

    // only 'out' being distributed means simulation is embarrasingly parallel, 
    // because the full 'in' is already known on every node
    if (outDist && !inDist)
        accel_densmatr_mixQureg_subD(outProb, out, inProb, in);
}


void localiser_densmatr_mixQureg(qreal outProb, Qureg out, qreal inProb, Qureg in) {