Check docs in linear

[Richard Roberts]

And this:

Does this

    /** Return the <em>upper-triangular part</em> of the full *augmented* information matrix,
     * as described above.  See HessianFactor class documentation above to explain that only the
     * upper-triangular part of the information matrix is stored and returned by this function.
     */
    SymmetricBlockMatrix::constBlock info() const { return info_.full(); }

now return a fully symmetric matrix ?

If so, is the transpose fill below still necessary?

  Matrix GaussianFactorGraph::augmentedHessian(
      boost::optional<const Ordering&> optionalOrdering) const {
    // combine all factors and get upper-triangular part of Hessian
    HessianFactor combined(*this, Scatter(*this, optionalOrdering));
    Matrix result = combined.info();
    // Fill in lower-triangular part of Hessian
    result.triangularView<Eigen::StrictlyLower>() = result.transpose();
    return result;
  }