# Circuit cutting on gpus **URL:** \ **Category:** PennyLane Help\ **Created:** [May 23, 2023, 1:42pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968 "2023-05-23T13:42:38Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Zohim\_Chandani1](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/zohim_chandani1/32/584_2.png) [@Zohim\_Chandani1](https://discuss.pennylane.ai/u/Zohim_Chandani1)\ **Post date:** [May 23, 2023, 1:42pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968/1 "2023-05-23T13:42:38Z")
I am able to simulate a 30 qubit circuit with the GPU backend. ```auto n_qubits = 30 dev = qml.device('lightning.gpu', wires=n_qubits) @qml.qnode(dev) def circuit(): for i in range(n_qubits): qml.X(wires=i) return qml.expval(qml.pauli.string_to_pauli_word("Z")) circuit() ``` However I get a out of memory error when I run 31 qubits which is expected: `PLException: [/project/pennylane_lightning_gpu/src/util/DataBuffer.hpp][Line:37][Method:DataBuffer]: Error in PennyLane Lightning: out of memory ` Given that my GPU can support 30 qubits, I would like to employ circuit cutting to simulate a 31 qubit circuit as shown below: ```auto n_qubits = 31 dev = qml.device('lightning.gpu', wires=n_qubits) @qml.cut_circuit(auto_cutter=True) @qml.qnode(dev) def circuit(): for i in range(n_qubits): qml.X(wires=i) return qml.expval(qml.pauli.string_to_pauli_word("Z")) circuit() PLException: [/project/pennylane_lightning_gpu/src/util/DataBuffer.hpp][Line:37][Method:DataBuffer]: Error in PennyLane Lightning: out of memory ``` Why does this approach not work? When I run circuit cutting for 15 qubits, I get the following error ```auto n_qubits = 15 dev = qml.device('lightning.gpu', wires=n_qubits) @qml.cut_circuit(auto_cutter=True) @qml.qnode(dev) def circuit(): for i in range(n_qubits): qml.X(wires=i) return qml.expval(qml.PauliZ(0)) circuit() --------------------------------------------------------------------------- UnboundLocalError Traceback (most recent call last) Cell In[11], line 14 9 qml.X(wires=i) 11 return qml.expval(qml.PauliZ(0)) ---> 14 circuit() File ~/.local/lib/python3.10/site-packages/pennylane/transforms/batch_transform.py:300, in batch_transform.default_qnode_wrapper.._wrapper(*args, **kwargs) 297 qnode.interface = qml.math.get_interface(*args, *list(kwargs.values())) 299 qnode.construct(args, kwargs) --> 300 tapes, processing_fn = self.construct(qnode.qtape, *targs, **tkwargs) 302 interface = qnode.interface 303 execute_kwargs = getattr(qnode, "execute_kwargs", {}).copy() File ~/.local/lib/python3.10/site-packages/pennylane/transforms/batch_transform.py:431, in batch_transform.construct(self, tape, *targs, **tkwargs) 429 if argnums is not None: 430 tape.trainable_params = argnums --> 431 tapes, processing_fn = self.transform_fn(tape, *targs, **tkwargs) 433 if processing_fn is None: 435 def processing_fn(x): File ~/.local/lib/python3.10/site-packages/pennylane/transforms/qcut/cutcircuit.py:349, in cut_circuit(tape, auto_cutter, use_opt_einsum, device_wires, max_depth, **kwargs) 342 except ImportError as e: 343 raise ImportError( 344 "The opt_einsum package is required when use_opt_einsum is set to " ... ---> 85 order += 1 # pylint: disable=undefined-loop-variable 86 for m in tape.measurements: 87 obs = getattr(m, "obs", None) UnboundLocalError: local variable 'order' referenced before assignment ``` ```auto Name: PennyLane Version: 0.30.0 Summary: PennyLane is a Python quantum machine learning library by Xanadu Inc. Home-page: https://github.com/XanaduAI/pennylane Author: Author-email: License: Apache License 2.0 Location: /home/cudaq/.local/lib/python3.10/site-packages Requires: appdirs, autograd, autoray, cachetools, networkx, numpy, pennylane-lightning, requests, rustworkx, scipy, semantic-version, toml Required-by: PennyLane-Lightning, PennyLane-Lightning-GPU, PennyLane-qiskit Platform info: Linux-5.4.0-146-generic-x86_64-with-glibc2.35 Python version: 3.10.6 Numpy version: 1.23.5 Scipy version: 1.10.1 Installed devices: - lightning.qubit (PennyLane-Lightning-0.30.0) - qiskit.aer (PennyLane-qiskit-0.30.0) - qiskit.basicaer (PennyLane-qiskit-0.30.0) - qiskit.ibmq (PennyLane-qiskit-0.30.0) - qiskit.ibmq.circuit_runner (PennyLane-qiskit-0.30.0) - qiskit.ibmq.sampler (PennyLane-qiskit-0.30.0) - default.gaussian (PennyLane-0.30.0) - default.mixed (PennyLane-0.30.0) - default.qubit (PennyLane-0.30.0) - default.qubit.autograd (PennyLane-0.30.0) - default.qubit.jax (PennyLane-0.30.0) - default.qubit.tf (PennyLane-0.30.0) - default.qubit.torch (PennyLane-0.30.0) - default.qutrit (PennyLane-0.30.0) - null.qubit (PennyLane-0.30.0) - lightning.gpu (PennyLane-Lightning-GPU-0.29.1) ``` Thanks a lot for your help ---
**Author:** ![isaacdevlugt](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/isaacdevlugt/32/1159_2.png) [@isaacdevlugt](https://discuss.pennylane.ai/u/isaacdevlugt)\ **Post date:** [May 23, 2023, 4:01pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968/2 "2023-05-23T16:01:58Z")
Hey @Zohim_Chandani1! You’re using `X` instead of `PauliX` 🙂. Try that out instead and see if that fixes things! ---
**Author:** ![Zohim\_Chandani1](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/zohim_chandani1/32/584_2.png) [@Zohim\_Chandani1](https://discuss.pennylane.ai/u/Zohim_Chandani1)\ **Post date:** [May 24, 2023, 4:02pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968/3 "2023-05-24T16:02:36Z")
Thats weird since the below with `X` executes without an error: ```auto n_qubits = 2 dev = qml.device('lightning.gpu', wires=n_qubits) @qml.qnode(dev) def circuit(): for i in range(n_qubits): qml.X(wires=i) return qml.expval(qml.PauliZ(0)) circuit() ``` ---
**Author:** ![Zohim\_Chandani1](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/zohim_chandani1/32/584_2.png) [@Zohim\_Chandani1](https://discuss.pennylane.ai/u/Zohim_Chandani1)\ **Post date:** [May 24, 2023, 4:12pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968/4 "2023-05-24T16:12:04Z")
Code snippet below throws up out of memory error. Shouldnt a 34q simulation be possible with circuit cutting? Thanks a lot ```auto n_qubits = 34 dev = qml.device('lightning.gpu', wires=n_qubits) @qml.cut_circuit(auto_cutter=True) @qml.qnode(dev) def circuit(): for i in range(n_qubits): qml.PauliX(wires=i) return qml.expval(qml.PauliZ(0)) circuit() ``` ```plaintext PLException Traceback (most recent call last) Cell In[4], line 3 1 n_qubits = 34 ----> 3 dev = qml.device('lightning.gpu', wires=n_qubits) 5 @qml.cut_circuit(auto_cutter=True) 6 @qml.qnode(dev) 7 def circuit(): 8 for i in range(n_qubits): File ~/.local/lib/python3.10/site-packages/pennylane/ __init__.py:326, in device(name, *args, **kwargs) 320 raise DeviceError( 321 f"The {name} plugin requires PennyLane versions {plugin_device_class.pennylane_requires}, " 322 f"however PennyLane version { __version__ } is installed." 323 ) 325 # Construct the device --> 326 dev = plugin_device_class(*args, **options) 328 # Once the device is constructed, we set its custom expansion function if 329 # any custom decompositions were specified. 330 if custom_decomps is not None: File ~/.local/lib/python3.10/site-packages/pennylane_lightning_gpu/lightning_gpu.py:217, in LightningGPU. __init__ (self, wires, sync, c_dtype, shots, batch_obs) 215 raise TypeError(f"Unsupported complex Type: {c_dtype}") 216 super(). __init__ (wires, shots=shots, r_dtype=r_dtype, c_dtype=c_dtype) --> 217 self._gpu_state = _gpu_dtype(c_dtype)(self.num_wires) 218 self._create_basis_state_GPU(0) 219 self._sync = sync PLException: [/project/pennylane_lightning_gpu/src/util/DataBuffer.hpp][Line:37][Method:DataBuffer]: Error in PennyLane Lightning: out of memory ``` ---
**Author:** ![isaacdevlugt](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/isaacdevlugt/32/1159_2.png) [@isaacdevlugt](https://discuss.pennylane.ai/u/isaacdevlugt)\ **Post date:** [May 24, 2023, 4:37pm UTC](https://discuss.pennylane.ai/t/circuit-cutting-on-gpus/2968/5 "2023-05-24T16:37:30Z")
> Thats weird since the below with `X` executes without an error: Yep! `X` is the position operator in continuous variables 😅. It’s still a pennylane operation 🙂. [https://docs.pennylane.ai/en/stable/code/api/pennylane.X.html?highlight=X](https://docs.pennylane.ai/en/stable/code/api/pennylane.X.html?highlight=X) > Shouldnt a 34q simulation be possible with circuit cutting? It really depends on the cutting procedure and the circuit itself. With the simple circuit you have, though, there’s not really a place to put a circuit cut. I think you’re maybe wanting the circuit to be separated into, for example, two 17-qubit circuits, which isn’t necessarily circuit cutting in spirit. You’ve created a product state — you don’t need a 34-qubit circuit, you can just create 34 different 1-qubit circuits.