sklearn.metrics.pairwise.rbf_kernel(X, Y=None, gamma=None)[source]

Compute the rbf (gaussian) kernel between X and Y.

K(x, y) = exp(-gamma ||x-y||^2)

for each pair of rows x in X and y in Y.

Read more in the User Guide.

Xndarray of shape (n_samples_X, n_features)

A feature array.

Yndarray of shape (n_samples_Y, n_features), default=None

An optional second feature array. If None, uses Y=X.

gammafloat, default=None

If None, defaults to 1.0 / n_features.

kernel_matrixndarray of shape (n_samples_X, n_samples_Y)

The RBF kernel.