circuit_knitting.utils.metrics.chi2_distance

chi2_distance(target, obs)

Measure the Chi-square distance.

The Chi-Square distance is a measure of statistically correlation between two feature vectors and is defined as $ sum_i frac{(x_i - y_i)^2}{x_i + y_i}$.

Deprecated since version 0.7.0: The function circuit_knitting.utils.metrics.chi2_distance() is deprecated as of circuit-knitting-toolbox 0.7.0. It will be removed no sooner than CKT v0.8.0.

Examples: >>> chi2_distance(np.array([0.1, 0.1, 0.3, 0.5]), np.array([0.25, 0.25, 0.25, 0.25])) 0.21645021645021645

>>> chi2_distance(np.array([0.25, 0.25, 0.25, 0.25]), np.array([0.25, 0.25, 0.25, 0.25]))
0

Parameters:

• target – The target feature vector

• obs – The actually observed feature vector

Returns:

The computed distance

Raises:

Exception – The target is not a numpy array or dictionary