[Bug]: RuntimeError: Index out of bounds

[necrosource-bot]

What happened?

I have snippet of code that works without problems on macOS but throws a RuntimeError on Linux/Windows.
So far, I haven't fully figured out what is going on, but what I observed:

• The MultiTaskGP.task_mapper is assigned [nan, 0]
• The above is perhaps still expected, but in GPyTorch, these nan values get translated into 9223372036854775808, i.e. some integer overflow is happening (the number is the -2ˆ63)

Please provide a minimal, reproducible example of the unexpected behavior.

import torch
from botorch.acquisition import qLogExpectedImprovement
from botorch.acquisition.objective import IdentityMCObjective
from botorch.models import MultiTaskGP
from botorch.optim import optimize_acqf_mixed

train_x = torch.tensor([[1.0, 10.0], [1.0, 20.0]])
train_y = torch.tensor([[10.0], [20.0]])
gp = MultiTaskGP(
    train_x,
    train_y,
    task_feature=0,
    output_tasks=[0, 1],
    all_tasks=[0, 1],
    validate_task_values=False,
)


acqf = qLogExpectedImprovement(gp, 0.0, objective=IdentityMCObjective())
bounds = torch.tensor([[0.0, 0.0], [1.0, 5.0]])
q = 1
num_restarts = 10
raw_samples = 64
fixed_features_list = [{0: 0}, {0: 1}]

candidate, acqf_value = optimize_acqf_mixed(
    acqf,
    bounds=bounds,
    q=q,
    num_restarts=num_restarts,
    raw_samples=raw_samples,
    fixed_features_list=fixed_features_list,
)

print(candidate)
print(acqf_value)

Please paste any relevant traceback/logs produced by the example provided.

RuntimeError: index -9223372036854775808 is out of bounds for dimension 2 with size 1

BoTorch Version

0.16.1

Python Version

3.10.19

Operating System

Linux/Windows

(Optional) Describe any potential fixes you've considered to the issue outlined above.

No response

Pull Request

None

Code of Conduct

• I agree to follow BoTorch's Code of Conduct