# Cutting: Difference between processing functions

**URL:** <https://discuss.pennylane.ai/t/cutting-difference-between-processing-functions/4789>\
**Category:** PennyLane Help\
**Created:** [June 22, 2024, 7:59pm UTC](https://discuss.pennylane.ai/t/cutting-difference-between-processing-functions/4789 "2024-06-22T19:59:56Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Nathaniel\_Tornow](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/nathaniel_tornow/32/2032_2.png) [@Nathaniel\_Tornow](https://discuss.pennylane.ai/u/Nathaniel_Tornow)\
**Post date:** [June 22, 2024, 7:59pm UTC](https://discuss.pennylane.ai/t/cutting-difference-between-processing-functions/4789/1 "2024-06-22T19:59:56Z")

</div>

Hi!

I have a question regarding the two circuit-cutting postprocessing functions [`qcut_processing_fn_sample`](https://docs.pennylane.ai/en/stable/code/api/pennylane.qcut.qcut_processing_fn_sample.html) and [`qcut_processing_fn_mc`](https://docs.pennylane.ai/en/stable/code/api/pennylane.qcut.qcut_processing_fn_mc.html):

Is `qcut_processing_fn_mc` with a postprocessing function `fn` the same as running `qcut_processing_fn_sample` and running `np.mean([fn(s) for s in samples])` on the resulting samples?

In particular, in the following example, they seem to be the same (or at least similar), but are they by definition?

```python
import pennylane as qml
from pennylane import numpy as np
from functools import partial

dev = qml.device("default.qubit", wires=2, shots=10000)

def fn(x):
    if x[0] == 0:
        return 1
    if x[0] == 1:
        return -1

@partial(qml.cut_circuit_mc, classical_processing_fn=fn)
@qml.qnode(dev)
def circuit(x):
    qml.RX(0.89, wires=0)
    qml.RY(0.5, wires=1)
    qml.RX(1.3, wires=2)

    qml.CNOT(wires=[0, 1])
    qml.WireCut(wires=1)
    qml.CNOT(wires=[1, 2])

    qml.RX(x, wires=0)
    qml.RY(0.7, wires=1)
    qml.RX(2.3, wires=2)
    return qml.sample(wires=[0, 1, 2])

@partial(qml.cut_circuit_mc)
@qml.qnode(dev)
def circuit2(x):
    qml.RX(0.89, wires=0)
    qml.RY(0.5, wires=1)
    qml.RX(1.3, wires=2)

    qml.CNOT(wires=[0, 1])
    qml.WireCut(wires=1)
    qml.CNOT(wires=[1, 2])

    qml.RX(x, wires=0)
    qml.RY(0.7, wires=1)
    qml.RX(2.3, wires=2)
    return qml.sample(wires=[0, 1, 2])

x = 2.90
res1 = circuit(x)

samples = circuit2(x)
res2 = np.mean([fn(s) for s in samples])

print(abs(res1-res2))

```

If they are the same per definition, what is the advantage of `qcut_processing_fn_mc` compared to `qcut_processing_fn_sample`?

Thank you!  
Nate

---

<div class="post-metadata">

**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\
**Post date:** [June 25, 2024, 10:08pm UTC](https://discuss.pennylane.ai/t/cutting-difference-between-processing-functions/4789/2 "2024-06-25T22:08:09Z")

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Hi @Nathaniel_Tornow , welcome to the Forum and thank you for your question!

Please see Tom’s answer [here](https://github.com/PennyLaneAI/pennylane/issues/5897#issuecomment-2189137325).

TLDR: we recommend using [`qcut_processing_fn_mc`](https://docs.pennylane.ai/en/stable/code/api/pennylane.qcut.qcut_processing_fn_mc.html).

Enjoy using PennyLane!