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from .... import tensor as mt
from .core import PairwiseDistances
from .euclidean import euclidean_distances
[docs]def rbf_kernel(X, Y=None, gamma=None):
"""
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 :ref:`User Guide <rbf_kernel>`.
Parameters
----------
X : tensor of shape (n_samples_X, n_features)
Y : tensor of shape (n_samples_Y, n_features)
gamma : float, default None
If None, defaults to 1.0 / n_features
Returns
-------
kernel_matrix : tensor of shape (n_samples_X, n_samples_Y)
"""
X, Y = PairwiseDistances.check_pairwise_arrays(X, Y)
if gamma is None:
gamma = 1.0 / X.shape[1]
K = euclidean_distances(X, Y, squared=True)
K *= -gamma
K = mt.exp(K)
return K