Hi Pytorch people,
I am currently trying to build a tensor iteratively in Pytorch. Sadly the backprop does not work with the inplace operation in the loop. I already tried equivalent programs with stack for example. Does somebody know how I could build the tensor with a working backprop?
This is a minimal example which produces the error:
import torch
k=2
a =torch.Tensor([10,20])
a.requires_grad_(True)
b = torch.Tensor([10,20])
b.requires_grad_(True)
batch_size = a.size()[0]
uniform_samples = Uniform(torch.tensor([0.0]), torch.tensor([1.0])).rsample(torch.tensor([batch_size,k])).view(-1,k)
exp_a = 1/a
exp_b = 1/b
km = (1- uniform_samples.pow(exp_b)).pow(exp_a)
sticks = torch.zeros(batch_size,k)
remaining_sticks = torch.ones_like(km[:,0])
for i in range(0,k-1):
sticks[:,i] = remaining_sticks * km[:,i]
remaining_sticks *= (1-km[:,i])
sticks[:,k-1] = remaining_sticks
latent_variables = sticks
latent_variables.sum().backward()
The stack trace:
/opt/conda/conda-bld/pytorch_1570910687230/work/torch/csrc/autograd/python_anomaly_mode.cpp:57: UserWarning: Traceback of forward call that caused the error:
File "/opt/conda/lib/python3.6/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "/opt/conda/lib/python3.6/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/opt/conda/lib/python3.6/site-packages/ipykernel_launcher.py", line 16, in <module>
app.launch_new_instance()
File "/opt/conda/lib/python3.6/site-packages/traitlets/config/application.py", line 664, in launch_instance
app.start()
File "/opt/conda/lib/python3.6/site-packages/ipykernel/kernelapp.py", line 563, in start
self.io_loop.start()
File "/opt/conda/lib/python3.6/site-packages/tornado/platform/asyncio.py", line 148, in start
self.asyncio_loop.run_forever()
File "/opt/conda/lib/python3.6/asyncio/base_events.py", line 438, in run_forever
self._run_once()
File "/opt/conda/lib/python3.6/asyncio/base_events.py", line 1451, in _run_once
handle._run()
File "/opt/conda/lib/python3.6/asyncio/events.py", line 145, in _run
self._callback(*self._args)
File "/opt/conda/lib/python3.6/site-packages/tornado/ioloop.py", line 690, in <lambda>
lambda f: self._run_callback(functools.partial(callback, future))
File "/opt/conda/lib/python3.6/site-packages/tornado/ioloop.py", line 743, in _run_callback
ret = callback()
File "/opt/conda/lib/python3.6/site-packages/tornado/gen.py", line 787, in inner
self.run()
File "/opt/conda/lib/python3.6/site-packages/tornado/gen.py", line 748, in run
yielded = self.gen.send(value)
File "/opt/conda/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 361, in process_one
yield gen.maybe_future(dispatch(*args))
File "/opt/conda/lib/python3.6/site-packages/tornado/gen.py", line 209, in wrapper
yielded = next(result)
File "/opt/conda/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 268, in dispatch_shell
yield gen.maybe_future(handler(stream, idents, msg))
File "/opt/conda/lib/python3.6/site-packages/tornado/gen.py", line 209, in wrapper
yielded = next(result)
File "/opt/conda/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 541, in execute_request
user_expressions, allow_stdin,
File "/opt/conda/lib/python3.6/site-packages/tornado/gen.py", line 209, in wrapper
yielded = next(result)
File "/opt/conda/lib/python3.6/site-packages/ipykernel/ipkernel.py", line 300, in do_execute
res = shell.run_cell(code, store_history=store_history, silent=silent)
File "/opt/conda/lib/python3.6/site-packages/ipykernel/zmqshell.py", line 536, in run_cell
return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
File "/opt/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2855, in run_cell
raw_cell, store_history, silent, shell_futures)
File "/opt/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2881, in _run_cell
return runner(coro)
File "/opt/conda/lib/python3.6/site-packages/IPython/core/async_helpers.py", line 68, in _pseudo_sync_runner
coro.send(None)
File "/opt/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3058, in run_cell_async
interactivity=interactivity, compiler=compiler, result=result)
File "/opt/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3249, in run_ast_nodes
if (await self.run_code(code, result, async_=asy)):
File "/opt/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3326, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-124-2bbdbc3af797>", line 16, in <module>
sticks[:,i] = remaining_sticks * km[:,i]
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-124-2bbdbc3af797> in <module>
19 latent_variables = sticks
20
---> 21 latent_variables.sum().backward()
/opt/conda/lib/python3.6/site-packages/torch/tensor.py in backward(self, gradient, retain_graph, create_graph)
148 products. Defaults to ``False``.
149 """
--> 150 torch.autograd.backward(self, gradient, retain_graph, create_graph)
151
152 def register_hook(self, hook):
/opt/conda/lib/python3.6/site-packages/torch/autograd/__init__.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
97 Variable._execution_engine.run_backward(
98 tensors, grad_tensors, retain_graph, create_graph,
---> 99 allow_unreachable=True) # allow_unreachable flag
100
101
RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation: [torch.FloatTensor [2]] is at version 1; expected version 0 instead. Hint: the backtrace further above shows the operation that failed to compute its gradient. The variable in question was changed in there or anywhere later. Good luck!