Hotfix/polytopesampler seed (#1968)

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## Motivation

During bugfixing, I came around the issue that setting a seed in `get_polytope_samples` is not leading to the same samples when called several times with the same seed. This PR fixes it.

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

Yes.

Pull Request resolved: #1968

Test Plan: Unit tests.

Reviewed By: saitcakmak

Differential Revision: D47993712

Pulled By: Balandat

fbshipit-source-id: 95b3e548e78609a5d6593addbba0cf7585a76120

botorch/utils/sampling.py

@@ -249,7 +249,9 @@ def sample_polytope(
     # pre-sample samples from hypersphere
     d = x0.size(0)
     # uniform samples from unit ball in d dims
-    Rs = sample_hypersphere(d=d, n=n_tot, dtype=A.dtype, device=A.device).unsqueeze(-1)
+    Rs = sample_hypersphere(
+        d=d, n=n_tot, dtype=A.dtype, device=A.device, seed=seed
+    ).unsqueeze(-1)
 
     # compute matprods in batch
     ARs = (A @ Rs).squeeze(-1)

test/utils/test_sampling.py

@@ -348,6 +348,29 @@ def test_sample_polytope(self):
                 self.assertTrue((more_samples <= bounds[1]).all())
                 self.assertTrue((more_samples >= bounds[0]).all())
 
+    def test_sample_polytope_with_seed(self):
+        for dtype in (torch.float, torch.double):
+            A = self.A.to(dtype)
+            b = self.b.to(dtype)
+            x0 = self.x0.to(dtype)
+            bounds = self.bounds.to(dtype)
+            for interior_point in [x0, None]:
+                sampler1 = self.sampler_class(
+                    inequality_constraints=(A, b),
+                    bounds=bounds,
+                    interior_point=interior_point,
+                    **self.sampler_kwargs,
+                )
+                sampler2 = self.sampler_class(
+                    inequality_constraints=(A, b),
+                    bounds=bounds,
+                    interior_point=interior_point,
+                    **self.sampler_kwargs,
+                )
+                samples1 = sampler1.draw(n=10, seed=42)
+                samples2 = sampler2.draw(n=10, seed=42)
+                self.assertTrue(torch.allclose(samples1, samples2))
+
     def test_sample_polytope_with_eq_constraints(self):
         for dtype in (torch.float, torch.double):
             A = self.A.to(dtype)