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Edge-case: fitting constant y values with decay analysis #487

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Merged
merged 2 commits into from
Nov 3, 2021
Merged

Edge-case: fitting constant y values with decay analysis #487

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ec09c12
handling for very slow decay
Nov 3, 2021
0a2f921
fix comment
Nov 3, 2021
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24 changes: 19 additions & 5 deletions qiskit_experiments/curve_analysis/standard_analysis/decay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,8 @@

from typing import List, Union

import numpy as np

import qiskit_experiments.curve_analysis as curve


Expand Down Expand Up @@ -69,16 +71,28 @@ def _generate_fit_guesses(

Returns:
List of fit options that are passed to the fitter function.

Raises:
AnalysisError: When the y data is likely constant.
"""
curve_data = self._data()

user_opt.p0.set_if_empty(base=curve.guess.min_height(curve_data.y)[0])

user_opt.p0.set_if_empty(
tau=-1 / curve.guess.exp_decay(curve_data.x, curve_data.y),
amp=curve.guess.max_height(curve_data.y)[0] - user_opt.p0["base"],
)

alpha = curve.guess.exp_decay(curve_data.x, curve_data.y)

if alpha != 0.0:
user_opt.p0.set_if_empty(
tau=-1 / alpha,
amp=curve.guess.max_height(curve_data.y)[0] - user_opt.p0["base"],
)
else:
# Likely there is no slope. Cannot fit constant line with this model.
# Set some large enough number against to the scan range.
user_opt.p0.set_if_empty(
tau=100 * np.max(curve_data.x),
amp=curve.guess.max_height(curve_data.y)[0] - user_opt.p0["base"],
)
return user_opt

def _evaluate_quality(self, fit_data: curve.FitData) -> Union[str, None]:
Expand Down
16 changes: 10 additions & 6 deletions qiskit_experiments/curve_analysis/standard_analysis/oscillation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -219,15 +219,19 @@ def _generate_fit_guesses(

# Set guess for decay parameter based on estimated frequency
if freq_guess > df:
user_opt.p0.set_if_empty(
tau=-1
/ curve.guess.oscillation_exp_decay(
curve_data.x, curve_data.y - user_opt.p0["base"], freq_guess=freq_guess
)
alpha = curve.guess.oscillation_exp_decay(
curve_data.x, curve_data.y - user_opt.p0["base"], freq_guess=freq_guess
)
else:
# Very low frequency. Assume standard exponential decay
user_opt.p0.set_if_empty(tau=-1 / curve.guess.exp_decay(curve_data.x, curve_data.y))
alpha = curve.guess.exp_decay(curve_data.x, curve_data.y)

if alpha != 0.0:
user_opt.p0.set_if_empty(tau=-1 / alpha)
else:
# Likely there is no slope. Cannot fit constant line with this model.
# Set some large enough number against to the scan range.
user_opt.p0.set_if_empty(tau=100 * np.max(curve_data.x))

user_opt.bounds.set_if_empty(
amp=[0, 1.5],
Expand Down