tfidf 是個非常普遍作用在文件檢索的功能，輸入為一個[i*j]的term-frequence的矩陣，輸出為[i*j]的tfidf值-tfidf has been applied on the task of text process. The input of the function is a [i*j] term-frquency matrix. The output is a [i*j] of which element is calculated by the tfidf measure.