"Bred vectors" are an example: https://en.wikipedia.org/wiki/Bred_vector https://en.wikipedia.org/wiki/Bred_vector Note that these vectors are generated not by

"Bred vectors" are an example: https://en.wikipedia.org/wiki/Bred_vector https://en.wikipedia.org/wiki/Bred_vector Note that these vectors are generated not by just sampling the uncertainty in I.C.'s. Of course, this is because the space of I.C. perturbations is too high-dimensional to cover. In the method above, selection of perturbation direction is based on the adjustments implied when new data is sync'ed to the model. There are other techniques.