Fix bug in tracking the number of device executions #1046
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Hello. You may have forgotten to update the changelog!
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| # actually run so she has full control. This could be done by changing the class | ||
| # of the user's device before and after executing the tape. | ||
| if self.device != self._original_device: | ||
| self._original_device._num_executions += 1 # pylint: disable=protected-access |
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This might sound crazy, but will self.qtape.execute(device=self.device) always result in just 1 additional execution?
Or is this a case where there could be more than 1 under the scenes?
I suppose I am being crazy
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I was wondering too. In future this may very well happen, but I think it does not happen at the moment. More reason to find a better fix one day.
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In that case you could do
diff_executions = self.device.num_executions
res = self.qtape.execute(device=self.device)
diff_executions = self.device.num_executions - diff_executions
if self.device is not self._original_device:
self._original_device._num_executions += diff_executions| return qml.expval(qml.PauliZ(0)) | ||
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| dev = qml.device("default.qubit", wires=2) | ||
| qn = QNode(func, dev, interface="autograd") |
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Should we add diff_method="backprop" here to be explicit, in case we ever change the logic?
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But if we change the logic and don't switch the device any more, we actually don't only want to test "backprop" either. Could do a fixture with all diff methods?
Co-authored-by: Josh Izaac <josh146@gmail.com>
Co-authored-by: Josh Izaac <josh146@gmail.com>
Codecov Report
@@ Coverage Diff @@
## master #1046 +/- ##
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Coverage 97.94% 97.94%
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Files 153 153
Lines 11481 11483 +2
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+ Hits 11245 11247 +2
Misses 236 236
Continue to review full report at Codecov.
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Context
With PR #1008 we are creating situations in which the tape is executed on a different device than the user has given to the qnode. This is a design issue we should access in the long term. In the short term it introduces a bug because the
num_executionsattribute is no longer tracked correctly on the user's device. This PR fixes the issue by manually adding1todevice.num_executionsif we are swapping out devices.It also adds some tests that would have caught the bug.
PS: Ignore the branch name!