A normalized kernel is one that, if given a data matrix that is all 1s, will
result in 1. This function applies a scalier multiple to the kernel to make
it normalized, if possible. Otherwise, it optionally warns and returns the
input kernel.
Usage
normalize_kernel(k, warning_enabled = TRUE)
Arguments
k
[matrix] The kernel.
warning_enabled
[logical] Whether to unable warnings, default
to TRUE.