Function getWhetherRealsAreStrictlyNonNegative

quest/src/core/utilities.cpp:712–734

 */

bool getWhetherRealsAreStrictlyNonNegative(qcomp* diags, qindex dim) {

    /// @todo
    /// consider multithreading or GPU-accelerating this
    /// when caller is big and e.g. has GPU memory

    // it may seem like this function should be combined with
    // getWhetherRealsAreApproxNonZero() above, or indeed with
    // getHermiticity(), since all three are relevant to vali-
    // dation of diagonl matrices which can be exponentiated.
    // Alas, such as design is complicated by this particular
    // property (non-negativeness) being independent of the
    // validation epsilon. For example, sometimes it needs to
    // be computed even when numerical validation is disabled,
    // and does not need recomputing with the epsilon changes.
    
    // check every real component is strictly >= 0
    for (qindex i=0; i<dim; i++)
        if (std::real(diags[i]) < 0)
            return false;

    return true;
}

// non-negativity of fixed-size matrices is always computed afresh
bool util_isStrictlyNonNegative(DiagMatr1 m) { return getWhetherRealsAreStrictlyNonNegative(m.elems, m.numElems); }