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-- Oct 17 In-Class Exercise Thread

(Edited: 2018-10-17)

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-- Oct 17 In-Class Exercise Thread

((resource:15398161090001899634694.jpg|Resource Description for 15398161090001899634694.jpg))

-- Oct 17 In-Class Exercise Thread

idf = log(N/N_t)

tf = f⋅(k1+1)/f+k1⋅((1−b)+b⋅(ld/lavg))

N_t = 1/64

f = 1

k = 1.2

log(64) * 5 * (1 * (k+1))/(1 + k) = 6 * 5 = 30

Part B

b = 0.75

log(64) * 5 * (1 * (k+1))/ (1 + k * ((1 - b) + b * (2)))

6 * 5 * (2.2)/(1 + 1.2(0.25 + 0.75(2)))

30 * (2.2)/(1 + 1.2(1.75))

30 * 2.2 / 3.1 = 21.29

idf = log(N/N_t) tf = f⋅(k1+1)/f+k1⋅((1−b)+b⋅(ld/lavg)) N_t = 1/64 f = 1 k = 1.2 log(64) * 5 * (1 * (k+1))/(1 + k) = 6 * 5 = 30 Part B b = 0.75 log(64) * 5 * (1 * (k+1))/ (1 + k * ((1 - b) + b * (2))) 6 * 5 * (2.2)/(1 + 1.2(0.25 + 0.75(2))) 30 * (2.2)/(1 + 1.2(1.75)) 30 * 2.2 / 3.1 = 21.29

-- Oct 17 In-Class Exercise Thread

IDF = log(N/N/64) = 6 1) TF1 = (5* 1 * (1.2+1))/ (1.2 +1) = 5 BM25 score = 6*5 = 30 2) TF2 = (5 * 1* (1.2 + 1))/(1 + 1.2 * (1+0.75)) = 3.55 BM25 score = 3.55 * 6 = 21.3

(Edited: 2018-10-17)

<nowiki> IDF = log(N/N/64) = 6 1) TF1 = (5* 1 * (1.2+1))/ (1.2 +1) = 5 BM25 score = 6*5 = 30 2) TF2 = (5 * 1* (1.2 + 1))/(1 + 1.2 * (1+0.75)) = 3.55 BM25 score = 3.55 * 6 = 21.3 </nowiki>

-- Oct 17 In-Class Exercise Thread

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-- Oct 17 In-Class Exercise Thread

ScoreBM25(q, d) = 5* log(64) * (k1+1) * 1/( 1+ k1) = 5 * 6 = 30 ScoreBM25(q, d) = 5 * log(64) * (k1+1) * 1/ ( 1+ k1* (1+b)) = 30 * 2.2 / (1+ 1.2 * 1.75) = 21.3

-- Oct 17 In-Class Exercise Thread

Given:

Query q = (t1, t2, t3, t4, t5)

Nt1 = Nt2 = Nt3 = Nt4 = Nt5 = N/64

ft1,d = ft2,d = ft3,d = ft4,d = ft5,d = 1

1)

ld = lavg

ScoreBM25(q, d) = 5*[log⁡(N/(N/64))*((1*(1.2+1))/(1+1.2((1-b)+b*1)))]

		     = 5*6
		     =30

2)

ld = 2*lavg

ScoreBM25(q, d) = 5*[log⁡(N/(N/64))*((1*(1.2+1))/(1+1.2((1-b)+b*2)))]

		     = 5*[log⁡(64)*(2.2/(1+1.2(1+0.75)))]
		     = 5*[6*0.709]
		     =21.29

(Edited: 2018-10-21)

Given: Query q = (t1, t2, t3, t4, t5) Nt1 = Nt2 = Nt3 = Nt4 = Nt5 = N/64 ft1,d = ft2,d = ft3,d = ft4,d = ft5,d = 1 1) ld = lavg ScoreBM25(q, d) = 5*[log⁡(N/(N/64))*((1*(1.2+1))/(1+1.2((1-b)+b*1)))] = 5*6 =30 2) ld = 2*lavg ScoreBM25(q, d) = 5*[log⁡(N/(N/64))*((1*(1.2+1))/(1+1.2((1-b)+b*2)))] = 5*[log⁡(64)*(2.2/(1+1.2(1+0.75)))] = 5*[6*0.709] =21.29

-- Oct 17 In-Class Exercise Thread

(Edited: 2018-10-22)

((resource:IMG_4452.jpg|Resource Description for IMG_4452.jpg))

-- Oct 17 In-Class Exercise Thread

Problem 1) Idf = log(64/1)=6 Tf = 5*(k1+1)/(1+k1)=5 Tf-Idf=30 Problem 2) Tf= 5*(k1+1)/(1+k1*(1-b+2b)) Tf-Idf=30(k1+1)/(k1+k1*b+1) =30(1.2+1)/(1.2+1.2*0.75+1) = 21.3