ValueError: KernelRidge alpha must be non-negative

ValueError: KernelRidge alpha must be >= 0

$ python -c "from sklearn.kernel_ridge import KernelRidge; KernelRidge(alpha=-1.0).fit([[0],[1]], [0,1])"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: alpha must be >= 0

Why this happens

Negative regularization is invalid.

Fix

Set alpha to >= 0.

Wrong code

from sklearn.kernel_ridge import KernelRidge
KernelRidge(alpha=-0.1)

Fixed code

from sklearn.kernel_ridge import KernelRidge
KernelRidge(alpha=1.0)