Add InfeasibilityError exception (#2652)

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## Motivation

Add customised error for infeasible problem. Details see #2631

### Have you read the [Contributing Guidelines on pull requests](https://github.com/pytorch/botorch/blob/main/CONTRIBUTING.md#pull-requests)?

Yes.

Pull Request resolved: #2652

Test Plan:
The customised error is tested in a similar way as the other customised errors.

## Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/pytorch/botorch, and link to your PR here.)

Reviewed By: saitcakmak

Differential Revision: D67280696

Pulled By: Balandat

fbshipit-source-id: 581dbe23d304966632c83feb1286071d7fbddade

botorch/exceptions/errors.py

@@ -86,3 +86,9 @@ def __init__(self, /, *args: Any, current_x: npt.NDArray, **kwargs: Any) -> None
         """
         super().__init__(*args, **kwargs)
         self.current_x = current_x
+
+
+class InfeasibilityError(BotorchError, ValueError):
+    r"""Exception raised when infeasibility occurs."""
+
+    pass

botorch/utils/sampling.py

@@ -27,7 +27,7 @@
 import numpy.typing as npt
 import scipy
 import torch
-from botorch.exceptions.errors import BotorchError
+from botorch.exceptions.errors import BotorchError, InfeasibilityError
 from botorch.exceptions.warnings import UserInputWarning
 from botorch.sampling.qmc import NormalQMCEngine
 from botorch.utils.transforms import unnormalize
@@ -249,7 +249,7 @@ def sample_polytope(
     """
     # Check that starting point satisfies the constraints.
     if not ((slack := A @ x0 - b) <= 0).all():
-        raise ValueError(
+        raise InfeasibilityError(
             f"Starting point does not satisfy the constraints. Inputs: {A=},"
             f"{b=}, {x0=}, A@x0-b={slack}."
         )
@@ -442,7 +442,7 @@ def find_interior_point(
         )
 
     if result.status == 2:
-        raise ValueError(
+        raise InfeasibilityError(
             "No feasible point found. Constraint polytope appears empty. "
             + "Check your constraints."
         )
@@ -524,7 +524,7 @@ def __init__(
             if self.feasible(interior_point):
                 self.x0 = interior_point
             else:
-                raise ValueError("The given input point is not feasible.")
+                raise InfeasibilityError("The given input point is not feasible.")
         else:
             self.x0 = self.find_interior_point()
 

test/exceptions/test_errors.py

@@ -11,6 +11,7 @@
     BotorchTensorDimensionError,
     CandidateGenerationError,
     DeprecationError,
+    InfeasibilityError,
     InputDataError,
     OptimizationGradientError,
     OptimizationTimeoutError,
@@ -28,6 +29,7 @@ def test_botorch_exception_hierarchy(self):
             InputDataError,
             UnsupportedError,
             BotorchTensorDimensionError,
+            InfeasibilityError,
         ]:
             self.assertIsInstance(ErrorClass(), BotorchError)
 
@@ -38,6 +40,7 @@ def test_raise_botorch_exceptions(self):
             CandidateGenerationError,
             InputDataError,
             UnsupportedError,
+            InfeasibilityError,
         ):
             with self.assertRaises(ErrorClass):
                 raise ErrorClass("message")