preliminary implementation of STL robustness

robustness.py

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+from functools import singledispatch
+from operator import sub, add
+
+from lenses import lens
+
+import stl.ast
+
+
+@singledispatch
+def pointwise_robustness(stl):
+    raise NotImplementedError
+
+
+@pointwise_robustness.register(stl.Or)
+def _(stl):
+    return lambda x, t: max(pointwise_robustness(arg)(x, t) for arg in stl.args)
+
+
+@pointwise_robustness.register(stl.And)
+def _(stl):
+    return lambda x, t: min(pointwise_robustness(arg)(x, t) for arg in stl.args)
+
+
+@pointwise_robustness.register(stl.F)
+def _(stl):
+    lo, hi = stl.interval
+    return lambda x, t: max(pointwise_robustness(stl.arg)(x, t + t2) 
+                            for t2 in x[lo:hi].index)
+
+
+@pointwise_robustness.register(stl.G)
+def _(stl):
+    lo, hi = stl.interval
+    return lambda x, t: min(pointwise_robustness(stl.arg)(x, t + t2) 
+                            for t2 in x[lo:hi].index)
+
+
+@pointwise_robustness.register(stl.Neg)
+def _(stl):
+    return lambda x, t: -pointwise_robustness(arg)(x, t)
+
+
+op_lookup = {
+    ">": sub,
+    ">=": sub,
+    "<": add,
+    "<=": add,
+    "=": lambda a, b: -abs(a - b),
+}
+
+
+@pointwise_robustness.register(stl.LinEq)
+def _(stl):
+    op = op_lookup[stl.op]
+    return lambda x, t: op(eval_terms(stl, x, t), stl.const)
+
+
+def eval_terms(lineq, x, t):
+    psi = lens(lineq).terms.each_().modify(eval_term(x, t))
+    return sum(psi.terms)
+
+
+def eval_term(x, t):
+    return lambda term: term.coeff*x[term.id.name][t]