scipy.stats.Covariance.colorize#

Covariance.colorize(x)[source]#

Perform a colorizing transformation on data.

“Colorizing” (“color” as in “colored noise”, in which different frequencies may have different magnitudes) transforms a set of uncorrelated random variables into a new set of random variables with the desired covariance. When a coloring transform is applied to a sample of points distributed according to a multivariate normal distribution with identity covariance and zero mean, the covariance of the transformed sample is approximately the covariance matrix used in the coloring transform.

Parameters:

xarray_like: An array of points. The last dimension must correspond with the dimensionality of the space, i.e., the number of columns in the covariance matrix.

Returns:

x_array_like: The transformed array of points.

References

[1]

“Whitening Transformation”. Wikipedia. https://en.wikipedia.org/wiki/Whitening_transformation

[2]

Novak, Lukas, and Miroslav Vorechovsky. “Generalization of coloring linear transformation”. Transactions of VSB 18.2 (2018): 31-35. DOI:10.31490/tces-2018-0013

Examples

>>> import numpy as np
>>> from scipy import stats
>>> rng = np.random.default_rng()
>>> n = 3
>>> A = rng.random(size=(n, n))
>>> cov_array = A @ A.T  # make matrix symmetric positive definite
>>> cholesky = np.linalg.cholesky(cov_array)
>>> cov_object = stats.Covariance.from_cholesky(cholesky)
>>> x = rng.multivariate_normal(np.zeros(n), np.eye(n), size=(10000))
>>> x_ = cov_object.colorize(x)
>>> cov_data = np.cov(x_, rowvar=False)
>>> np.allclose(cov_data, cov_array, rtol=3e-2)
True