DOC Use LaTeX for phi in KernelCenterer user manual
@@ -250,10 +250,10 @@ Centering kernel matrices
-------------------------
If you have a kernel matrix of a kernel :math:`K` that computes a dot product
-in a feature space defined by function :math:`phi`,
+in a feature space defined by function :math:`\phi`,
a :class:`KernelCenterer` can transform the kernel matrix
so that it contains inner products in the feature space
-defined by :math:`phi` followed by removal of the mean in that space.
+defined by :math:`\phi` followed by removal of the mean in that space.
.. _preprocessing_transformer:
