Why .cuda() always allocate GPU:0?

Only b.to(device) can move b to GPU:1?

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if u have 4 graphic cards,u can choose which one to use.
By deault it will be cuda:0

I have two,so is there a way to change the default gpu?

you can try this
torch.cuda.set_device(1)

It’s easier to use the flag CUDA_VISIBLE_DEVICES=‘1’ rather than coding using set_device.

If you need that it means you are working with a single gpu.

You can call .cuda(idx) which allocates in the gpu you want if you use several gpus.

CUDA_VISIBLE_DEVICES=“1” exposes only 1 GPU for the program. However, when torch uses the GPUS it starts ordering from 0. So GPU 1 on system is mapped to GPU 0 in the program.