# Where did sublinear tf-idf originate?

I have often come across this weighting scheme for tf-idf (term frequency - inverse document frequency) in text mining. I am wondering where it came from (for citations). I've searched very rigorously, but can't seem to find anything. Specifically, this is the weighting scheme:

$${\rm tfidf}(t,d,D)=(1+\log({f_{t,d})})\cdot \log\!\bigg(1+\frac{N}{n_t}\bigg) \\ N=|D|$$

where $t$ is the query term, $d$ is the document, $D$ is set of documents, $n_t$ is the document frequency of $t$, $f_{t,d}$ is how many times $t$ appears in $d$

• Please describe what all the notation in the equation means. – Greenparker May 15 '16 at 0:01
• What's your question? Is it just a reference request? – Sycorax May 15 '16 at 19:40
• @C11H17N2O2SNa Yes. Where did this come from? – aces May 15 '16 at 20:05