Function printQuregAutoDeployments

quest/src/api/environment.cpp:329–385

void printQuregAutoDeployments(bool isDensMatr) {

    // build all table rows dynamically before print
    std::vector<std::tuple<string, string>> rows;

    // we will get auto-deployment for every possible number of qubits; silly but cheap and robust!
    int useDistrib,  useGpuAccel,  useMulti;
    int prevDistrib, prevGpuAccel, prevMulti;

    // assume all deployments disabled for 1 qubit
    prevDistrib  = 0;
    prevGpuAccel = 0;
    prevMulti    = 0;

    // test to theoretically max #qubits, surpassing max that can fit in RAM and GPUs, because
    // auto-deploy will still try to deploy there to (then subsequent validation will fail)
    int maxQubits = mem_getMaxNumQuregQubitsBeforeGlobalMemSizeofOverflow(isDensMatr, globalEnvPtr->numNodes);

    for (int numQubits=1; numQubits<maxQubits; numQubits++) {

        // re-choose auto deployment
        useDistrib  = modeflag::USE_AUTO;
        useGpuAccel = modeflag::USE_AUTO;
        useMulti    = modeflag::USE_AUTO;;
        autodep_chooseQuregDeployment(numQubits, isDensMatr, useDistrib, useGpuAccel, useMulti, *globalEnvPtr);

        // skip if deployments are unchanged
        if (useDistrib  == prevDistrib  &&
            useGpuAccel == prevGpuAccel &&
            useMulti    == prevMulti)
            continue; 

        // else prepare string summarising the new deployments (trailing space is fine)
        string value = "";
        if (useMulti)
            value += "[omp] "; // ordered by #qubits to attempt consistent printed columns
        if (useGpuAccel)
            value += "[gpu] ";
        if (useDistrib)
            value += "[mpi] ";

        // log the #qubits of the deployment change
        rows.push_back({printer_toStr(numQubits) + " qubits", value});

        // skip subsequent qubits with the same deployments
        prevDistrib  = useDistrib;
        prevGpuAccel = useGpuAccel;
        prevMulti    = useMulti;
    }

    // tailor table title to type of Qureg
    string prefix = (isDensMatr)? "density matrix" : "statevector";
    string title = prefix + " autodeployment";
    rows.empty()?
        print_table(title, "(no parallelisations available)"):
        print_table(title, rows);
}