Hi @ptrblck , thanks for your quick reply.
I solved my problem.
I think that the problem was a pytorch version issue. I am trying to use for what I do pytorch 1.9.1
I found out that between previous versions of torch and mine (pytorch 1.9.1) the functions
torch.floor() and torch.ceil() return different types. For pytorch 1.4.0 they returned an int while now they return a tensor.
Therefore, the solution to my problem was to change (in the file CenterFusion/src/lib/utils/pointcloud.py) the lines:
    bbox_int = torch.tensor([torch.floor(bbox[0]), 
                         torch.floor(bbox[1]), 
                         torch.ceil(bbox[2]), 
                         torch.ceil(bbox[3])], dtype=torch.int32)# format: xyxy

to
    bbox_int = torch.tensor([int(torch.floor(bbox[0])), 
                         int(torch.floor(bbox[1])), 
                         int(torch.ceil(bbox[2])), 
                         int(torch.ceil(bbox[3]))], dtype=torch.int32)# format: xyxy

Does it sound reasonable?
Thanks for the help!