GPU error & other things

[cymqqqq]

Hi.I got a problem here:
When I run train.py,error exists:
Traceback (most recent call last):
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1356, in _do_call
return fn(*args)
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1339, in _run_fn
self._extend_graph()
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1374, in _extend_graph
tf_session.ExtendSession(self._session)
tensorflow.python.framework.errors_impl.InvalidArgumentError: Cannot assign a device for operation model_1/ones: {{node model_1/ones}}was explicitly assigned to /device:GPU:0 but available devices are [ /job:localhost/replica:0/task:0/device:CPU:0, /job:localhost/replica:0/task:0/device:XLA_CPU:0, /job:localhost/replica:0/task:0/device:XLA_GPU:0, /job:localhost/replica:0/task:0/device:XLA_GPU:1, /job:localhost/replica:0/task:0/device:XLA_GPU:2, /job:localhost/replica:0/task:0/device:XLA_GPU:3 ]. Make sure the device specification refers to a valid device.
[[model_1/ones]]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "train.py", line 203, in
sess.run(initializer)
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 950, in run
run_metadata_ptr)
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1173, in _run
feed_dict_tensor, options, run_metadata)
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1350, in _do_run
run_metadata)
File "/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py", line 1370, in _do_call
raise type(e)(node_def, op, message)
tensorflow.python.framework.errors_impl.InvalidArgumentError: Cannot assign a device for operation model_1/ones: node model_1/ones (defined at /home/CYM/pixel-cnn/pixel_cnn_pp/model.py:36) was explicitly assigned to /device:GPU:0 but available devices are [ /job:localhost/replica:0/task:0/device:CPU:0, /job:localhost/replica:0/task:0/device:XLA_CPU:0, /job:localhost/replica:0/task:0/device:XLA_GPU:0, /job:localhost/replica:0/task:0/device:XLA_GPU:1, /job:localhost/replica:0/task:0/device:XLA_GPU:2, /job:localhost/replica:0/task:0/device:XLA_GPU:3 ]. Make sure the device specification refers to a valid device.
[[model_1/ones]]
should I reinstall the tensorflow-gpu? I don't know why.
and another problem in train.py ,line 172:
x = np.cast[np.float32]((x - 127.5) / 127.5) # input to pixelCNN is scaled from uint8 [0,255] to float in range [-1,1]
you say "input to pixelCNN is scaled from uint8 [0,255] to float in range [-1,1]"
why do this operation? can you explain
thx!