The loss curves in the scenario calculator are reproducible only by accident

[Michele Simionato]

Currently the numbers produced by the risk scenario calculator are reproducible, but only because we are reading the ground motion fields in a fixed order. Even simple refactorings of the hazard getters will return the GMFs in a different order and produce different numbers, unless extra care is taken. The extra care consists in keeping the relative order of GMFs and epsilons consistent. The problem is exercised in the following test case in risklib.tests.scientific_test:

 class MeanLossTestCase(unittest.TestCase):
    def test_mean_loss(self):
        vf = scientific.VulnerabilityFunction(
            'PGA', imls=[0.1, 0.2, 0.3, 0.5, 0.7],
            mean_loss_ratios=[0.0035, 0.07, 0.14, 0.28, 0.56],
            covs=[0.1, 0.2, 0.3, 0.4, 0.5])

        epsilons = [0.98982371, 0.2776809, -0.44858935, 0.96196624,
                    -0.82757864, 0.53465707, 1.22838619]
        imls = [0.280357, 0.443609, 0.241845, 0.506982, 0.459758,
                0.456199, 0.38077]
        mean = vf.apply_to([imls], [epsilons])[0].mean()
        aaae(mean, 0.2318058254)

        # if you don't reorder the epsilons, the mean loss depends by
        # the order of the imls!
        reordered_imls = [0.443609, 0.280357, 0.241845, 0.506982, 0.459758,
                          0.456199, 0.38077]
        mean2 = vf.apply_to([reordered_imls], [epsilons])[0].mean()
        aaae(mean2, 0.238145174018)

        # by reordering the epsilons the problem is solved
        reordered_epsilons = [0.2776809, 0.98982371, -0.44858935, 0.96196624,
                              -0.82757864, 0.53465707, 1.22838619]
        mean3 = vf.apply_to([reordered_imls], [reordered_epsilons])[0].mean()
        aaae(mean3, mean)

On the engine side, one must ensure that the epsilons are correctly associated to the GMFs.

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-risklib/pull/75

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-engine/pull/1506