DOC clarify that sklearn.metric.pairwise doesn't provide callables for pairwise_kernel
@@ -1678,8 +1678,11 @@ def pairwise_kernels(X, Y=None, metric="linear", filter_params=False,
If metric is "precomputed", X is assumed to be a kernel matrix.
Alternatively, if metric is a callable function, it is called on each
pair of instances (rows) and the resulting value recorded. The callable
- should take two arrays from X as input and return a value indicating
- the distance between them.
+ should take two rows from X as input and return the corresponding
+ kernel value as a single number. This means that callables from
+ `sklearn.metrics.pairwise` are not allowed, as they operate on
+ matrices, not single samples. Use the string identifying the kernel
+ instead.
filter_params : boolean
Whether to filter invalid parameters or not.
