Add a helper for evaluating feasibility of candidate points (#2733)

Summary:
Pull Request resolved: #2733

Pull Request resolved: #2565

Adds a helper for evaluating the feasibility of parameter constraints on a `batch x q x d` tensor of candidates.

A follow-up diff will utilize this to detect infeasible candidates produced during optimization and raise an error rather than returning infeasible points to the user.

Reviewed By: esantorella

Differential Revision: D63909338

fbshipit-source-id: 873ba5036a7076b718ec5e3f054b6f0f3fb999c2

botorch/optim/optimize.py

@@ -1438,7 +1438,7 @@ def optimize_acqf_discrete_local_search(
         X_avoid = torch.zeros(0, dim, device=device, dtype=dtype)
 
     inequality_constraints = inequality_constraints or []
-    for i in range(q):
+    for _ in range(q):
         # generate some starting points
         X0 = _gen_starting_points_local_search(
             discrete_choices=discrete_choices,

botorch/optim/parameter_constraints.py

@@ -11,7 +11,6 @@
 from __future__ import annotations
 
 from collections.abc import Callable
-
 from functools import partial
 from typing import Union
 
@@ -26,7 +25,7 @@
 ScipyConstraintDict = dict[
     str, Union[str, Callable[[np.ndarray], float], Callable[[np.ndarray], np.ndarray]]
 ]
-NLC_TOL = -1e-6
+CONST_TOL = 1e-6
 
 
 def make_scipy_bounds(
@@ -511,9 +510,12 @@ def f_grad(X):
 
 
 def nonlinear_constraint_is_feasible(
-    nonlinear_inequality_constraint: Callable, is_intrapoint: bool, x: Tensor
+    nonlinear_inequality_constraint: Callable,
+    is_intrapoint: bool,
+    x: Tensor,
+    tolerance: float = CONST_TOL,
 ) -> Tensor:
-    """Checks if a nonlinear inequality constraint is fulfilled.
+    """Checks if a nonlinear inequality constraint is fulfilled (within tolerance).
 
     Args:
         nonlinear_inequality_constraint: Callable to evaluate the
@@ -523,14 +525,17 @@ def nonlinear_constraint_is_feasible(
             constraint has to evaluated over the whole q-batch and is a an
             inter-point constraint.
         x: Tensor of shape (batch x q x d).
+        tolerance: Rather than using the exact `const(x) >= 0` constraint, this helper
+            checks feasibility of `const(x) >= -tolerance`. This avoids marking the
+            candidates as infeasible due to tiny violations.
 
     Returns:
         A boolean tensor of shape (batch) indicating if the constraint is
         satified by the corresponding batch of `x`.
     """
 
     def check_x(x: Tensor) -> bool:
-        return _arrayify(nonlinear_inequality_constraint(x)).item() >= NLC_TOL
+        return _arrayify(nonlinear_inequality_constraint(x)).item() >= -tolerance
 
     x_flat = x.view(-1, *x.shape[-2:])
     is_feasible = torch.ones(x_flat.shape[0], dtype=torch.bool, device=x.device)
@@ -603,3 +608,82 @@ def make_scipy_nonlinear_inequality_constraints(
             shapeX=shapeX,
         )
     return scipy_nonlinear_inequality_constraints
+
+
+def evaluate_feasibility(
+    X: Tensor,
+    inequality_constraints: list[tuple[Tensor, Tensor, float]] | None = None,
+    equality_constraints: list[tuple[Tensor, Tensor, float]] | None = None,
+    nonlinear_inequality_constraints: list[tuple[Callable, bool]] | None = None,
+    tolerance: float = CONST_TOL,
+) -> Tensor:
+    r"""Evaluate feasibility of candidate points (within a tolerance).
+
+    Args:
+        X: The candidate tensor of shape `batch x q x d`.
+        inequality_constraints: A list of tuples (indices, coefficients, rhs),
+            with each tuple encoding an inequality constraint of the form
+            `\sum_i (X[indices[i]] * coefficients[i]) >= rhs`. `indices` and
+            `coefficients` should be torch tensors. See the docstring of
+            `make_scipy_linear_constraints` for an example. When q=1, or when
+            applying the same constraint to each candidate in the batch
+            (intra-point constraint), `indices` should be a 1-d tensor.
+            For inter-point constraints, in which the constraint is applied to the
+            whole batch of candidates, `indices` must be a 2-d tensor, where
+            in each row `indices[i] =(k_i, l_i)` the first index `k_i` corresponds
+            to the `k_i`-th element of the `q`-batch and the second index `l_i`
+            corresponds to the `l_i`-th feature of that element.
+        equality_constraints: A list of tuples (indices, coefficients, rhs),
+            with each tuple encoding an equality constraint of the form
+            `\sum_i (X[indices[i]] * coefficients[i]) = rhs`. See the docstring of
+            `make_scipy_linear_constraints` for an example.
+        nonlinear_inequality_constraints: A list of tuples representing the nonlinear
+            inequality constraints. The first element in the tuple is a callable
+            representing a constraint of the form `callable(x) >= 0`. In case of an
+            intra-point constraint, `callable()`takes in an one-dimensional tensor of
+            shape `d` and returns a scalar. In case of an inter-point constraint,
+            `callable()` takes a two dimensional tensor of shape `q x d` and again
+            returns a scalar. The second element is a boolean, indicating if it is an
+            intra-point or inter-point constraint (`True` for intra-point. `False` for
+            inter-point). For more information on intra-point vs inter-point
+            constraints, see the docstring of the `inequality_constraints` argument.
+        tolerance: The tolerance used to check the feasibility of equality constraints
+            and non-linear inequality constraints. For equality constraints, we check
+            if `abs(const(X) - rhs) < tolerance`. For non-linear inequality constraints,
+            we check if `const(X) >= -tolerance`. This avoids marking the candidates as
+            infeasible due to tiny violations.
+
+    Returns:
+        A boolean tensor of shape `batch` indicating if the corresponding candidate of
+        shape `q x d` is feasible.
+    """
+    is_feasible = torch.ones(X.shape[:-2], device=X.device, dtype=torch.bool)
+    if inequality_constraints is not None:
+        for idx, coef, rhs in inequality_constraints:
+            if idx.ndim == 1:
+                # Intra-point constraints.
+                is_feasible &= ((X[..., idx] * coef).sum(dim=-1) >= rhs).all(dim=-1)
+            else:
+                # Inter-point constraints.
+                is_feasible &= (X[..., idx[:, 0], idx[:, 1]] * coef).sum(dim=-1) >= rhs
+    if equality_constraints is not None:
+        for idx, coef, rhs in equality_constraints:
+            if idx.ndim == 1:
+                # Intra-point constraints.
+                is_feasible &= (
+                    ((X[..., idx] * coef).sum(dim=-1) - rhs).abs() < tolerance
+                ).all(dim=-1)
+            else:
+                # Inter-point constraints.
+                is_feasible &= (
+                    (X[..., idx[:, 0], idx[:, 1]] * coef).sum(dim=-1) - rhs
+                ).abs() < tolerance
+    if nonlinear_inequality_constraints is not None:
+        for const, intra in nonlinear_inequality_constraints:
+            is_feasible &= nonlinear_constraint_is_feasible(
+                nonlinear_inequality_constraint=const,
+                is_intrapoint=intra,
+                x=X,
+                tolerance=tolerance,
+            )
+    return is_feasible

test/optim/test_parameter_constraints.py

@@ -18,6 +18,7 @@
     _make_linear_constraints,
     _make_nonlinear_constraints,
     eval_lin_constraint,
+    evaluate_feasibility,
     lin_constraint_jac,
     make_scipy_bounds,
     make_scipy_linear_constraints,
@@ -529,6 +530,142 @@ def test_generate_unfixed_lin_constraints(self):
                     eq=eq,
                 )
 
+    def test_evaluate_feasibility(self) -> None:
+        # Check that the feasibility is evaluated correctly.
+        X = torch.tensor(  # 3 x 2 x 3 -> leads to output of shape 3.
+            [
+                [[1.0, 1.0, 1.0], [1.0, 1.0, 3.0]],
+                [[2.0, 2.0, 1.0], [2.0, 2.0, 5.0]],
+                [[3.0, 3.0, 3.0], [3.0, 3.0, 3.0]],
+            ],
+            device=self.device,
+        )
+        # X[..., 2] * 4 >= 5.
+        inequality_constraints = [
+            (
+                torch.tensor([2], device=self.device),
+                torch.tensor([4], device=self.device),
+                5.0,
+            )
+        ]
+        # X[..., 0] + X[..., 1] == 4.
+        equality_constraints = [
+            (
+                torch.tensor([0, 1], device=self.device),
+                torch.ones(2, device=self.device),
+                4.0,
+            )
+        ]
+
+        # sum(X, dim=-1) < 5.
+        def nlc1(x):
+            return 5 - x.sum(dim=-1)
+
+        # Only inequality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                inequality_constraints=inequality_constraints,
+            ),
+            torch.tensor([False, False, True], device=self.device),
+        )
+        # Only equality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                equality_constraints=equality_constraints,
+            ),
+            torch.tensor([False, True, False], device=self.device),
+        )
+        # Both inequality and equality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                inequality_constraints=inequality_constraints,
+                equality_constraints=equality_constraints,
+            ),
+            torch.tensor([False, False, False], device=self.device),
+        )
+        # Nonlinear inequality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                nonlinear_inequality_constraints=[(nlc1, True)],
+            ),
+            torch.tensor([True, False, False], device=self.device),
+        )
+        # No constraints.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+            ),
+            torch.ones(3, device=self.device, dtype=torch.bool),
+        )
+
+    def test_evaluate_feasibility_inter_point(self) -> None:
+        # Check that inter-point constraints evaluate correctly.
+        X = torch.tensor(  # 3 x 2 x 3 -> leads to output of shape 3.
+            [
+                [[1.0, 1.0, 1.0], [0.0, 1.0, 3.0]],
+                [[1.0, 1.0, 1.0], [2.0, 1.0, 3.0]],
+                [[2.0, 2.0, 1.0], [2.0, 2.0, 5.0]],
+            ],
+            dtype=torch.double,
+            device=self.device,
+        )
+        linear_inter_cons = (  # X[..., 0, 0] - X[..., 1, 0] >= / == 0.
+            torch.tensor([[0, 0], [1, 0]], device=self.device),
+            torch.tensor([1.0, -1.0], device=self.device),
+            0,
+        )
+        # Linear inequality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                inequality_constraints=[linear_inter_cons],
+            ),
+            torch.tensor([True, False, True], device=self.device),
+        )
+        # Linear equality.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                equality_constraints=[linear_inter_cons],
+            ),
+            torch.tensor([False, False, True], device=self.device),
+        )
+        # Linear equality with too high of a tolerance.
+        self.assertAllClose(
+            evaluate_feasibility(
+                X=X,
+                equality_constraints=[linear_inter_cons],
+                tolerance=100,
+            ),
+            torch.tensor([True, True, True], device=self.device),
+        )
+
+        # Nonlinear inequality.
+        def nlc1(x):  # X.sum(over q & d) >= 10.0
+            return x.sum() - 10.0
+
+        self.assertEqual(
+            evaluate_feasibility(
+                X=X,
+                nonlinear_inequality_constraints=[(nlc1, False)],
+            ).tolist(),
+            [False, False, True],
+        )
+        # All together.
+        self.assertEqual(
+            evaluate_feasibility(
+                X=X,
+                inequality_constraints=[linear_inter_cons],
+                equality_constraints=[linear_inter_cons],
+                nonlinear_inequality_constraints=[(nlc1, False)],
+            ).tolist(),
+            [False, False, True],
+        )
+
 
 class TestMakeScipyBounds(BotorchTestCase):
     def test_make_scipy_bounds(self):