Function canonicalize_rw 

pub fn canonicalize_rw(
    read_fraction: Option<&Distribution>,
    write_fraction: Option<&Distribution>,
) -> Result<Canonical>

Resolve the read_fraction / write_fraction pair into a canonical distribution. Exactly one must be Some.

When write_fraction is provided, each fraction fw is converted to a read fraction as 1.0 - fw.

Errors

Returns an error if both parameters are None, both are Some, or if canonicalization of the provided distribution fails.