# Issue with Quantum Fisher Information Matrix Calculation When Specifying argnum **URL:** https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492 **Category:** PennyLane Help **Created:** [November 5, 2024, 2:22pm UTC](https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492 "2024-11-05T14:22:20Z") **Posts on this page:** 4 **Page:** 1
### Author: ![a.rozgonyi96](https://avatars.discourse-cdn.com/v4/letter/a/3ec8ea/32.png) [@a.rozgonyi96](https://discuss.pennylane.ai/u/a.rozgonyi96) #### Post date: [November 5, 2024, 2:22pm UTC](https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492/1 "2024-11-05T14:22:20Z")
Hello PennyLane Community, I am currently working on calculating the Quantum Fisher Information Matrix (QFIM) for specific parameters. of the quantum circuit using the `qml.gradients.quantum_fisher` function. However, I am encountering an issue when I specify the `argnum` argument to indicate which variables I want the QFIM to be calculated for. Despite following the documentation, I receive an error message that seems related to the way I am specifying the parameters. I would greatly appreciate your guidance on this matter. Here is the code I am using, along with the error message I receive: ```auto import numpy as np import pennylane as qml from pennylane import numpy as pnp pnp.random.seed(42) N_qubits=3 # No. qubits dev = qml.device('default.qubit', wires=N_qubits) # Fixed values for each term in the Hamiltonian coeffs = [0.1, 0.2, -0.3] # This is a_i for each term thetas = pnp.array([1., 2., 3.]) # This is theta_i for each term params = pnp.array([0.5, 0.2, 0.1]) # This is parameters for circuit # Define the corresponding Pauli operators (observables) observables = [qml.Z(0), qml.Z(1), qml.Z(2)] # Construct the Hamiltonian hamiltonian = qml.Hamiltonian(coeffs, observables) # Define the quantum circuit with the Hamiltonian evolution @qml.qnode(dev) def encoding_circuit(theta, param): # Apply the unitary evolution U = exp(-i * H) qml.Hadamard(0) qml.CNOT(wires=(0,1)) qml.CNOT(wires=(0,2)) qml.RZ(theta[0], wires=0) qml.RZ(theta[1], wires=1) qml.RZ(theta[2], wires=2) qml.RX(param[0], wires=0) qml.RX(param[1], wires=1) qml.RX(param[2], wires=2) return qml.expval(hamiltonian) # Run the circuit and print the resulting state qfim = qml.gradients.quantum_fisher(encoding_circuit, argnum=[0])(thetas, params) qfim ``` The full error message is ```auto --------------------------------------------------------------------------- TypeError Traceback (most recent call last) in () 41 42 # Run the circuit and print the resulting state ---> 43 qfim = qml.gradients.quantum_fisher(encoding_circuit, argnum=[0])(thetas, params) 44 qfim 6 frames /usr/local/lib/python3.10/dist-packages/pennylane/transforms/core/transform_dispatcher.py in __call__ (self, *targs, **tkwargs) 93 if isinstance(obj, qml.tape.QuantumScript): 94 if self._expand_transform: ---> 95 expanded_tapes, expand_processing = self._expand_transform(obj, *targs, **tkwargs) 96 transformed_tapes = [] 97 processing_and_sclices = [] TypeError: _expand_trainable_multipar() got an unexpected keyword argument 'argnum' ``` Here it is the version that I use: ```auto Name: PennyLane Version: 0.38.0 Summary: PennyLane is a cross-platform Python library for quantum computing, quantum machine learning, and quantum chemistry. Train a quantum computer the same way as a neural network. Home-page: https://github.com/PennyLaneAI/pennylane Author: Author-email: License: Apache License 2.0 Location: /usr/local/lib/python3.10/dist-packages Requires: appdirs, autograd, autoray, cachetools, networkx, numpy, packaging, pennylane-lightning, requests, rustworkx, scipy, toml, typing-extensions Required-by: PennyLane_Lightning Platform info: Linux-6.1.85+-x86_64-with-glibc2.35 Python version: 3.10.12 Numpy version: 1.26.4 Scipy version: 1.13.1 Installed devices: - default.clifford (PennyLane-0.38.0) - default.gaussian (PennyLane-0.38.0) - default.mixed (PennyLane-0.38.0) - default.qubit (PennyLane-0.38.0) - default.qubit.autograd (PennyLane-0.38.0) - default.qubit.jax (PennyLane-0.38.0) - default.qubit.legacy (PennyLane-0.38.0) - default.qubit.tf (PennyLane-0.38.0) - default.qubit.torch (PennyLane-0.38.0) - default.qutrit (PennyLane-0.38.0) - default.qutrit.mixed (PennyLane-0.38.0) - default.tensor (PennyLane-0.38.0) - null.qubit (PennyLane-0.38.0) - lightning.qubit (PennyLane_Lightning-0.38.0) ``` ---
### 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: [November 6, 2024, 11:12pm UTC](https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492/2 "2024-11-06T23:12:22Z")
Hi @a.rozgonyi96, welcome to the Forum! If you remove `argnum=[0]` you will get the output for both `thetas` and `params`, where `qfim[0]` corresponds to the Quantum Fisher Information Matrix for `thetas`. So if you only wanted this output you could do: `print(qfim[0])` Would this be what you were looking for? An alternative would be to use param as a global variable instead of an argument but this may not work for a more general program. ```auto @qml.qnode(dev) def encoding_circuit(theta): param = params # Apply the unitary evolution U = exp(-i * H) qml.Hadamard(0) qml.CNOT(wires=(0,1)) qml.CNOT(wires=(0,2)) qml.RZ(theta[0], wires=0) qml.RZ(theta[1], wires=1) qml.RZ(theta[2], wires=2) qml.RX(param[0], wires=0) qml.RX(param[1], wires=1) qml.RX(param[2], wires=2) return qml.expval(hamiltonian) # Run the circuit and print the resulting state qfim = qml.gradients.quantum_fisher(encoding_circuit)(thetas) qfim ``` Let me know if this helps! ---
### Author: ![a.rozgonyi96](https://avatars.discourse-cdn.com/v4/letter/a/3ec8ea/32.png) [@a.rozgonyi96](https://discuss.pennylane.ai/u/a.rozgonyi96) #### Post date: [November 7, 2024, 11:19am UTC](https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492/3 "2024-11-07T11:19:42Z")
Thank you @CatalinaAlbornoz , it solved my problem perfectly. ---
### 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: [November 7, 2024, 10:42pm UTC](https://discuss.pennylane.ai/t/issue-with-quantum-fisher-information-matrix-calculation-when-specifying-argnum/7492/4 "2024-11-07T22:42:16Z")
I’m glad to hear @a.rozgonyi96 ! Enjoy using PennyLane!