# Problem in chalange 1 (Comparing expectation values)

"Hello everyone,

I hope you’re all doing well. I am trying to solve the challenges of Pennylane. However, I encountered problems with the first one. In the Python Kernel of Pennylane, my code is not working. But when I use the same code in my Jupyter notebook (including the test case checker), it works, and the test case checker approves the solution. Can someone help me?

import json
import pennylane as qml
import pennylane.numpy as np

dev = qml.device(‘default.qubit’,wires=1)# Define your device

@qml.qnode(dev)
def circuit1(angles):
“”"
A Qnode implementing the circuit shown in the top part of the image

``````Args:
angles (np.ndarray(float)): A list [theta_1, theta_2] of angle
parameters for the RX and RY gates respectively

Returns:
(np.tensor): The expectation value of the PauliX observable
"""

#  #
qml.RX(angles[0],wires=0)
qml.RY(angles[1],wires=0)
# Return the expectation value
return qml.expval(qml.PauliX(0))
``````

@qml.qnode(dev)
def circuit2(angles):
“”"
A Qnode implementing the circuit shown in the bottom part of the image

``````Args:
angles (np.ndarray(float)): A list [theta_1, theta_2] of angle
parameters for the RX and RY gates respectively

Returns:
(np.tensor): The expectation value of the PauliX observable
"""

# Put your code here #
qml.RY(angles[1],wires=0)
qml.RX(angles[0],wires=0)
# Return the expectation value
return qml.expval(qml.PauliX(0))
``````

def compare_circuits(angles):
“”"
Given two angles, compare two circuit outputs that have their order of
operations flipped: RX then RY VERSUS RY then RX.

``````Args:
angles (np.ndarray(float)): An array of two angles [theta_1, theta_2]

Returns:
(float): The absolute value of the difference between the expectation
values of the circuits.
"""

# Put your code here #
return abs(circuit1(angles) - circuit2(angles))
# Return the required difference in expectation values
#angles = [3.79894785, 0.71678115]
#compare_circuits(angles)
``````

# These functions are responsible for testing the solution.

def run(test_case_input: str) → str:
output = compare_circuits(ins)

``````return str(output)
``````

def check(solution_output: str, expected_output: str) → None:
assert np.isclose(solution_output, expected_output, rtol=1e-4)

# These are the public test cases

test_cases = [
(‘[3.79894785, 0.71678115]’, ‘1.177019’),
(‘[5.88344281, 0.30672784]’, ‘0.023805’)
]

# This will run the public test cases locally

for i, (input_, expected_output) in enumerate(test_cases):
print(f"Running test case {i} with input ‘{input_}’…")

``````try:
output = run(input_)

except Exception as exc:
print(f"Runtime Error. {exc}")

else:
if message := check(output, expected_output):
print(f"Wrong Answer. Have: '{output}'. Want: '{expected_output}'.")

else:
print("Correct!")
``````

My Output is :
Running test case 0 with input ‘[3.79894785, 0.71678115]’…
Correct!
Running test case 1 with input ‘[5.88344281, 0.30672784]’…
Correct!

Hey @Leandro , welcome to the forum!
Could I ask you to use this button

in a new line so you can copy in your code? That way we can copy-paste it and test it out easily for you, too.

Also, could you explain what you mean when you say the code doesn’t work in the PennyLane Python kernel? Do you get an error message? Also, if you could share the output of your `qml.about()`, that would be great!