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HooVer: a statistical model checking tool with optimistic optimization

NOTE: For reviewers who want to reproduce the results in the paper, please see Reproduce.md.

HooVer uses optimistic optimization to solve statistical model checking problems for MDPs.

Requirements

HooVer uses Python 3. To install the requirements:

pip3 install -r requirements.txt

Usage

usage: check.py [-h] [--model MODEL] [--args ARGS [ARGS ...]]
                  [--nRuns NRUNS] [--budget BUDGET] [--rho_max RHO_MAX]
                  [--sigma SIGMA] [--nHOOs NHOOS] [--batch_size BATCH_SIZE]
                  [--output OUTPUT] [--seed SEED]

optional arguments:
  -h, --help            show this help message and exit
  --model MODEL         models available: ConceptualModel |
                        DetectingPedestrian | Merging | Mlplatoon | MyModel |
                        Slplatoon (default: Slplatoon)
  --args ARGS [ARGS ...]
                        <Optional> This can be used to pass special arguments
                        to the model.
  --nRuns NRUNS         Number of repetitions. (default: 1)
  --budget BUDGET       Budget for total number of simulations. (default: 1e6)
  --rho_max RHO_MAX     Smoothness parameter. (default: 0.6)
  --sigma SIGMA         <Optional> Sigma parameter for UCB. If not specified,
                        it will be sqrt(0.5*0.5/batch_size).
  --nHOOs NHOOS         Number of HOO instances to use. (default: 4)
  --batch_size BATCH_SIZE
                        Batch size. (default: 100)
  --output OUTPUT       Path to save the results. (default: ./output.pklz)
  --seed SEED           Random seed for reproducibility. (default: 1024)

For example, to check the toy model, run the following command:

python3 check.py --model MyModel --budget 100000

You will find the following in the output, which is the most unsafe initial state:

...
optimal_xs: [array([1.97460938, 2.99414062])]
...

Verify your own model

The users can create their own model file, put it into the models/ folder, and mofify models/__init__.py correspondingly. For example, one can create models/MyModel.py and run HooVer with python3 check.py --model MyModel --budget 100000.

In the model file, the user has to create a class which is a subclass of NiMC. Here, we take models/MyModel.py as an example:

class MyModel(NiMC):
    def __init__(self, sigma, k=10):
        super(MyModel, self).__init__()

Then the user has to specify several essential components for this model. First, the user has to set the time bound k and the initial states set Theta by calling set_k() and set_Theta() respectively:

        self.set_Theta([[1,2],[2,3]])
        self.set_k(k)

The above code defines an intial state space \Theta = { (x,y) | x \in [1,2], y \in [2,3] }.

Then, the user has to implement the function is_usafe() which is used to check whether a state is unsafe. This function should return True if the state is unsafe and return False otherwise:

    def is_unsafe(self, state):
        if np.linalg.norm(state) > 4:
            return True # return unsafe if norm of the state is greater than 4.
        return False # return safe otherwise.```

Finally, the user has to specifing the transition kernel of the model by implementing the function transition(). For example, the following code in models/MyModel.py describes a random motion system:

    def transition(self, state):
        state = np.array(state)
        # increment is a 2-dimensional
        # normally distributed vector
        increment = self.sigma * np.random.randn(2)
        state += increment
        state = state.tolist()
        return state # return the new state

The user also has to update models/__init__.py by adding a line to import the new model file. For example, from .MyModel import *.

Acknowledgements

The MFTreeSearchCV code base was developed by Rajat Sen: ( https://github.com/rajatsen91/MFTreeSearchCV ) which in-turn was built on the blackbox optimization code base of Kirthivasan Kandasamy: ( https://github.com/kirthevasank )

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