Logging

The Python interface for Fulqrum has verbose logging functionality built in. Here we show an example of logging inside the Jupyter notebook from which this docuement is generated.

import fulqrum as fq

Formatting the logger

Here we show how to format the logger for useful output. Importantly, when using Jupyter notebooks we need to include force=True in the config in order to have the logs show up in the cell output

import logging

logging.basicConfig(
    level=logging.INFO,
    force=True,
    format="%(asctime)s - %(levelname)s - %(name)s - %(message)s",
)

Small example

Here we load a molecule, transform it, build a subspace, and finally put them all together in a SubspaceHamiltonian. Having set the logging config above, the ouput from each logger entry will be displayed in the cell output.

fop = fq.FermionicOperator.from_json("./data/lih.json")
op = fop.extended_jw_transformation()

counts = []
for kk in range(2**op.width):
    counts.append(bin(kk)[2:].zfill(op.width))

S = fq.Subspace([counts])
Hsub = fq.SubspaceHamiltonian(op, S)

2026-08-20 17:43:19,387 - INFO - fulqrum.core.fermi_operator - Extended JW time: 2.099 ms
2026-08-20 17:43:19,389 - INFO - fulqrum.core.subspace - Initializing Subspace
2026-08-20 17:43:19,390 - INFO - fulqrum.core.subspace - Full subspace bit-strings
2026-08-20 17:43:19,390 - INFO - fulqrum.core.subspace - Subspace size: 4096
2026-08-20 17:43:19,391 - INFO - fulqrum.core.subspace - Number of bits: 12
2026-08-20 17:43:19,391 - INFO - fulqrum.core.subspace - Using all bitset blocks: True
2026-08-20 17:43:19,392 - INFO - fulqrum.core.subspace - Reserve multiplier: 2
2026-08-20 17:43:19,393 - INFO - fulqrum.core.subspace - Subspace total init time: 3.342 ms
2026-08-20 17:43:19,394 - INFO - fulqrum.core.linear_operator - Initializing SubspaceHamiltonian
2026-08-20 17:43:19,394 - INFO - fulqrum.core.linear_operator - Number of qubits: 12
2026-08-20 17:43:19,396 - INFO - fulqrum.core.linear_operator - Num. diagonal terms 78
2026-08-20 17:43:19,396 - INFO - fulqrum.core.linear_operator - Num. off-diagonal terms 552
2026-08-20 17:43:19,397 - INFO - fulqrum.core.qubit_operator - Term grouping time: 0.225 ms
2026-08-20 17:43:19,397 - INFO - fulqrum.core.linear_operator - Term grouping time: 0.875 ms
2026-08-20 17:43:19,398 - INFO - fulqrum.core.qubit_operator - Starting ladder int grouping, ladder_width = 2
2026-08-20 17:43:19,398 - INFO - fulqrum.core.qubit_operator - Ladder int grouping time: 0.141 ms
2026-08-20 17:43:19,399 - INFO - fulqrum.core.linear_operator - Num. off-diagonal groups: 83
2026-08-20 17:43:19,399 - INFO - fulqrum.core.spmv - Initializing FulqrumSpMV
2026-08-20 17:43:19,399 - INFO - fulqrum.core.spmv - Operator is real
2026-08-20 17:43:19,400 - INFO - fulqrum.core.spmv - Operator type = 2
2026-08-20 17:43:19,400 - INFO - fulqrum.core.spmv - FulqrumSpMV total init time: 0.864 ms
2026-08-20 17:43:19,401 - INFO - fulqrum.core.linear_operator - SubspaceHamiltonian total init time: 6.412 ms