State that Evolution has matrix if target is Hamiltonian
#4768
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albi3ro
commented
Nov 1, 2023
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #4768 +/- ##
==========================================
- Coverage 99.64% 99.64% -0.01%
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Files 381 381
Lines 34305 34048 -257
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mudit2812
approved these changes
Nov 1, 2023
timmysilv
approved these changes
Nov 1, 2023
Co-authored-by: lillian542 <38584660+lillian542@users.noreply.github.com>
timmysilv
pushed a commit
that referenced
this pull request
Nov 8, 2023
We discovered a difference between `default.qubit` and
`default.qubit.legacy` over their treatment of the evolution of
hamiltonians:
```python
dev = qml.device('default.qubit', wires=3)
coeffs = [0.1, 0.2]
operators = [qml.PauliZ(0) @ qml.PauliZ(1), qml.PauliZ(0) @ qml.PauliZ(2)]
hamiltonian = qml.Hamiltonian(coeffs, operators)
@qml.qnode(dev)
def f():
qml.evolve(hamiltonian, 0.5)
return qml.density_matrix([0])
f()
```
Previously `qml.evolve(hamiltonain, t)` worked because `Evolution` was
hardcoded as an accepted observable. This meant it became an accepted
operation as well, even though it stated it didn't have a matrix.
In `ScalarSymbolicOp`, the parent for `Evolution`, we added a special
logical pathway for the matrix if the target is a Hamiltonian, but we
didn't include that special logical pathway for the `has_matrix`
property.
This PR updates the `has_matrix` property for and allows the evolution
of a hamiltonian to execute on `default.qubit`.
**Warning:**
This matrix is not backprop compatible.
```
dev = qml.device('default.qubit.legacy', wires=3)
coeffs = [0.1, 0.2]
operators = [qml.PauliZ(0) @ qml.PauliZ(1), qml.PauliZ(0) @ qml.PauliZ(2)]
@qml.qnode(dev)
def f(x):
hamiltonian = qml.Hamiltonian(x, operators)
qml.evolve(hamiltonian, 0.5)
return qml.density_matrix([0])
qml.grad(f)(qml.numpy.array(coeffs))
```
Gives
```
AttributeError: 'ArrayBox' object has no attribute 'tocsr'
```
`qml.dot` and operator arithemetic does not have these problems.
---------
Co-authored-by: lillian542 <38584660+lillian542@users.noreply.github.com>
timmysilv
added a commit
that referenced
this pull request
Nov 8, 2023
**Context:** These three bugs were identified as good to be released in a bugfix. **Description of the Change:** Cherry-pick the 3 commits to master onto this branch for the 0.33.1 bugfix release **Benefits:** Fixed bugs pushed out! **Possible Drawbacks:** Extra work in a critical time. **Related GitHub Issues:** #4768, #4781, #4787 --------- Co-authored-by: Christina Lee <christina@xanadu.ai> Co-authored-by: lillian542 <38584660+lillian542@users.noreply.github.com> Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com> Co-authored-by: Mudit Pandey <mudit.pandey@xanadu.ai>
|
[sc-50818] |
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We discovered a difference between
default.qubitanddefault.qubit.legacyover their treatment of the evolution of hamiltonians:Previously
qml.evolve(hamiltonain, t)worked becauseEvolutionwas hardcoded as an accepted observable. This meant it became an accepted operation as well, even though it stated it didn't have a matrix.In
ScalarSymbolicOp, the parent forEvolution, we added a special logical pathway for the matrix if the target is a Hamiltonian, but we didn't include that special logical pathway for thehas_matrixproperty.This PR updates the
has_matrixproperty for and allows the evolution of a hamiltonian to execute ondefault.qubit.Warning:
This matrix is not backprop compatible.
Gives
qml.dotand operator arithemetic does not have these problems.