sklearn.metrics.pairwise.chi2_kernel¶

sklearn.metrics.pairwise.chi2_kernel(X, Y=None, gamma=1.0)[source]¶

Computes the exponential chi-squared kernel X and Y.

The chi-squared kernel is computed between each pair of rows in X and Y. X and Y have to be non-negative. This kernel is most commonly applied to histograms.

The chi-squared kernel is given by:

k(x, y) = exp(-gamma Sum [(x - y)^2 / (x + y)])

It can be interpreted as a weighted difference per entry.

Read more in the User Guide.

Parameters

Xarray-like of shape (n_samples_X, n_features)

Yarray of shape (n_samples_Y, n_features)

gammafloat, default=1.

Scaling parameter of the chi2 kernel.

Returns

kernel_matrixarray of shape (n_samples_X, n_samples_Y)

See also

additive_chi2_kernel

The additive version of this kernel

sklearn.kernel_approximation.AdditiveChi2Sampler

A Fourier approximation to the additive version of this kernel.

References

• Zhang, J. and Marszalek, M. and Lazebnik, S. and Schmid, C. Local features and kernels for classification of texture and object categories: A comprehensive study International Journal of Computer Vision 2007 https://research.microsoft.com/en-us/um/people/manik/projects/trade-off/papers/ZhangIJCV06.pdf