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Sublinear tf scaling

It seems unlikely that twenty occurrences of a term in a document truly carry twenty times the significance of a single occurrence. Accordingly, there has been considerable research into variants of term frequency that go beyond counting the number of occurrences of a term. A common modification is to use instead the logarithm of the term frequency, which assigns a weight given by

1+\log \mbox{tf}...
...x{tf}_{t,d}>0 \\
0 & \mbox{otherwise}
\end{displaymath} (28)

In this form, we may replace $\mbox{tf}$ by some other function $\mbox{wf}$ as in (28), to obtain:

\mbox{wf-idf}_{t,d} = \mbox{wf}_{t,d} \times \mbox{idf}_t.
\end{displaymath} (29)

Equation (23) can then be modified by replacing tf-idf by wf-idf as defined in (29).

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