# Introduction to Machine Learning Nptel Week 3 Answers

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## Table of Contents

**Introduction to Machine Learning Nptel Week 3 Answers (July-Dec 2024)**

**Q1**.For a two-class problem using discriminant functions (δ discriminant function for class k

), where is the separating hyperplane located?

Where δ1>δ2

Where δ1<δ2

**Where δ1=δ2**

Where δ1+δ2=1

**Answer: Where δ1=δ2**

**Q2. **Given the following dataset consisting of two classes, A and B ,calculate the prior probability of each class.

What are the prior probabilities of class A and class B ?

P(A)=0.5,P(B)=0.5

**P(A)=0.625,P(B)=0.375**

P(A)=0.375,P(B)=0.625

P(A)=0.6,P(B)=0.4

**Answer: P(A)=0.625,P(B)=0.375**

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**Q3**.In a 3-class classification problem using linear regression, the output vectors for three data points are [0.8, 0.3, -0.1], [0.2, 0.6, 0.2], and [-0.1, 0.4, 0.7]. To which classes would these points be assigned?

1, 2, 1

1, 2, 2

1, 3, 2**1, 2, 3**

**Answer: 1, 2, 3**

**Q4.**If you have a 5-class classification problem and want to avoid masking using polynomial regression, what is the minimum degree of the polynomial you should use?

3**4**5

6

**Answer: 4**

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**Q5. **Consider a logistic regression model where the predicted probability for a given data point is 0.4. If the actual label for this data point is 1, what is the contribution of this data point to the log-likelihood?

-1.3219**-0.9163**

+1.3219

+0.9163

**Answer: -0.9163**

**Q6.**What additional assumption does LDA make about the covariance matrix in comparison to the basic assumption of Gaussian class conditional density?

The covariance matrix is diagonal

The covariance matrix is identity**The covariance matrix is the same for all classes**

The covariance matrix is different for each class

**Answer: The covariance matrix is the same for all classes**

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Q7.What is the shape of the decision boundary in LDA?

Quadratic**Linear**

Circular

Can not be determined

**Answer: Linear**

**Q8.**For two classes C1 and C2 with within-class variances σ2w1=1 and σ2w2=4 respectively, if the projected means are µ′1=1 and µ′2=3 , what is the Fisher criterion J(w) ?

0.5**0.8**

1.25

1.5

**Answer: 0.8**

Q9.Given two classes C1 and C2 with means µ1=[23] and µ2=[57] respectively, what is the direction vector w for LDA when the within-class covariance matrix Sw is the identity matrix I ?

**[43]**

[57]

[0.70.7]

[0.60.8]

**Answer: [43]**

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Q1. Which of the following statement(s) about decision boundaries and discriminant functions of classifiers is/are true?

In a binary classification problem, all points x on the decision boundary satisfy δ1(x)=δ2(x)

In a three-class classification problem, all points on the decision boundary satisfy δ1(x) = δ2(x) = δ3(x)

In a three-class classification problem, all points on the decision boundary satisfy at least one of δ1(x) = δ2(x), δ2(x) = δ3(x) or δ3(x) = δ1(x).

Let the input space be Rn. If x does not lie on the decision boundary, there exists an ϵ>0 such that all inputs y satisfying ||y−x||<ϵ belong to the same class.

**Answer: A, B, D**

**Q2. The following table gives the binary ground truth labels yi for four input points xi (not given). We have a logistic regression model with some parameter values that computes the probability p(xi) that the label is 1. Compute the likelihood of observing the data given these model parameters.**

0.346

0.230

0.058

0.086

**Answer: 0.230**

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**Q3. Which of the following statement(s) about logistic regression is/are true?**

It learns a model for the probability distribution of the data points in each class.

The output of a linear model is transformed to the range (0, 1) by a sigmoid function.

The parameters are learned by optimizing the mean-squared loss.

The loss function is optimized by using an iterative numerical algorithm.

**Answer: b, d**

**Q4. Consider a modified form of logistic regression given below where k is a positive constant and β0 and β1 are parameters.log(1−p(x)/kp(x))=β0−β1xThen find p(x).**

eβ0/keβ0+eβ1x

eβ1x/eβ0+keβ1x

eβ1x/keβ0+eβ1x

eβ1x/keβ0+e−β1x

**Answer: c. eβ1x/keβ0+eβ1x**

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**Q5. Consider a Bayesian classifier for a 3-class classification problem. The following tables give the class-conditioned density fk(x) for three classes k=1,2,3 at some point x in the input space.Note that πk denotes the prior probability of class k. Which of the following statement(s) about the predicted label at x is/are true?**

If the three classes have equal priors, the prediction must be class 2

If π3<π2 and π1<π2, the prediction may not necessarily be class 2

If π1>2π2, the prediction could be class 1 or class 3

If π1>π2>π3, the prediction must be class 1

**Answer: a, c**

**Q6. The following table gives the binary labels (y(i)) for four points (x(i)1,x(i)2) where i = 1,2,3,4. Among the given options, which set of parameter values β0,β1,β2 of a standard logistic regression model p(xi)=1/1+e−(β0+β1x+β2x) results in the highest likelihood for this data?**

β0=0.5,β1=1.0,β2=2.0

β0=−0.5,β1=−1.0,β2=2.0

β0=0.5,β1=1.0,β2=−2.0

β0=−0.5,β1=1.0,β2=2.0

**Answer: c. β0=0.5,β1=1.0,β2=−2.0**

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**Q7. Which of the following statement(s) about a two-class LDA model is/are true?**

It is assumed that the class-conditioned probability density of each class is a Gaussian

A different covariance matrix is estimated for each class

At a given point on the decision boundary, the class-conditioned probability densities corresponding to both classes must be equal

At a given point on the decision boundary, the class-conditioned probability densities corresponding to both classes may or may not be equal

**Answer: A, D**

**Q8. Consider the following two datasets and two LDA models trained respectively on these datasets.Dataset A: 100 samples of class 0; 50 samples of class 1Dataset B: 100 samples of class 0 (same as Dataset A); 100 samples of class 1 created by repeating twice the class 1 samples from Dataset AThe classifier is defined as follows in terms of the decision boundary wTx+b=0. Here, w is called the slope and b is called the intercept.x={0 if wTx+b<0 1 if wTx+b≥0**

**Which of the given statement is true?**

The learned decision boundary will be the same for both models

The two models will have the same slope but different intercepts

The two models will have different slopes but the same intercept

The two models may have different slopes and different intercepts

**Answer: The two models will have the same slope but different intercepts**

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These are Introduction to Machine Learning Nptel Week 3 Answers

**Q9. Which of the following statement(s) about LDA is/are true?**

It minimizes the between-class variance relative to the within-class variance

It maximizes the between-class variance relative to the within-class variance

Maximizing the Fisher information results in the same direction of the separating hyperplane as the one obtained by equating the posterior probabilities of classes

Maximizing the Fisher information results in a different direction of the separating hyperplane from the one obtained by equating the posterior probabilities of classes

**Answer: b, c**

**Q10. Which of the following statement(s) regarding logistic regression and LDA is/are true for a binary classification problem?**

For any classification dataset, both algorithms learn the same decision boundary

Adding a few outliers to the dataset is likely to cause a larger change in the decision boundary of LDA compared to that of logistic regression

Adding a few outliers to the dataset is likely to cause a similar change in the decision boundaries of both classifiers

If the within-class distributions deviate significantly from the Gaussian distribution, logistic regression is likely to perform better than LDA

**Answer: b, c**

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**Q1. Which of the following are differences between LDA and Logistic Regression?**

Logistic Regression is typically suited for binary classification, whereas LDA is directly applicable to multi-class problems

Logistic Regression is robust to outliers whereas LDA is sensitive to outliers

both (a) and (b)

None of these

**Answer: both (a) and (b)**

**Q2. We have two classes in our dataset. The two classes have the same mean but different variance.**

LDA can classify them perfectly.

LDA can NOT classify them perfectly.

LDA is not applicable in data with these properties

Insufficient information

**Answer: LDA can NOT classify them perfectly.**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q3. We have two classes in our dataset. The two classes have the same variance but different mean.**

LDA can classify them perfectly.

LDA can NOT classify them perfectly.

LDA is not applicable in data with these properties

Insufficient information

**Answer: Insufficient information**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q4. Given the following distribution of data points:What method would you choose to perform Dimensionality Reduction?**

Linear Discriminant Analysis

Principal Component Analysis

Both LDA and/or PCA.

None of the above.

**Answer: Linear Discriminant Analysis**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q5. If log(1−p(x)1+p(x))=β0+βxWhat is p(x)?**

a. p(x)=1+eβ0+βxeβ0+βx

b. p(x)=1+eβ0+βx1−eβ0+βx

c. p(x)=eβ0+βx1+eβ0+βx

d. p(x)=1−eβ0+βx1+eβ0+βx

**Answer: d. p(x)=1−eβ0+βx1+eβ0+βx**

**These are Introduction to Machine Learning Nptel Week 3 Answers**

**Q6. For the two classes ’+’ and ’-’ shown below.While performing LDA on it, which line is the most appropriate for projecting data points?**

Red

Orange

Blue

Green

**Answer: Blue**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q7. Which of these techniques do we use to optimise Logistic Regression:**

Least Square Error

Maximum Likelihood

(a) or (b) are equally good

(a) and (b) perform very poorly, so we generally avoid using Logistic Regression

None of these

**Answer: Maximum Likelihood**

**These are Introduction to Machine Learning Nptel Week 3 Answers**

**Q8. LDA assumes that the class data is distributed as:**

Poisson

Uniform

Gaussian

LDA makes no such assumption.

**Answer: Gaussian**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q9. Suppose we have two variables, X and Y (the dependent variable), and we wish to find their relation. An expert tells us that relation between the two has the form Y=meX+c. Suppose the samples of the variables X and Y are available to us. Is it possible to apply linear regression to this data to estimate the values of m and c?**

No.

Yes.

Insufficient information.

None of the above.

**Answer: Yes.**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q10. What might happen to our logistic regression model if the number of features is more than the number of samples in our dataset?**

It will remain unaffected

It will not find a hyperplane as the decision boundary

It will over fit

None of the above

**Answer: It will over fit**

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**Q1. Which of the following is false about a logistic regression based classifier?**

a. The logistic function is non-linear in the weights

b. The logistic function is linear in the weights

c. The decision boundary is non-linear in the weights

d. The decision boundary is linear in the weights

**Answer: b, c**

**Q2. Consider the case where two classes follow Gaussian distribution which are cen- tered at (3, 9) and (−3, 3) and have identity covariance matrix. Which of the following is the separating decision boundary using LDA assuming the priors to be equal?**

a. y−x=3

b. x+y=3

c. x+y=6

d. both (b) and (c)

e. None of the above

f. Can not be found from the given information

**Answer: c. x+y=6**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q3. Consider the following relation between a dependent variable and an independent variable identified by doing simple linear regression. Which among the following relations between the two variables does the graph indicate?**

a. as the independent variable increases, so does the dependent variable

b. as the independent variable increases, the dependent variable decreases

c. if an increase in the value of the dependent variable is observed, then the independent variable will show a corresponding increase

d. if an increase in the value of the dependent variable is observed, then the independent variable will show a corresponding decrease

e. the dependent variable in this graph does not actually depend on the independent variable

f. none of the above

**Answer: e. the dependent variable in this graph does not actually depend on the independent variable**

**Q4. Given the following distribution of data points:**

**What method would you choose to perform Dimensionality Reduction?**

a. Linear Discriminant Analysis

b. Principal Component Analysis

**Answer: a. Linear Discriminant Analysis**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q5. In general, which of the following classification methods is the most resistant to gross outliers?**

a. Quadratic Discriminant Analysis (QDA)

b. Linear Regression

c. Logistic regression

d. Linear Discriminant Analysis (LDA)

**Answer: c. Logistic regression**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q6. Suppose that we have two variables, X and Y (the dependent variable). We wish to find the relation between them. An expert tells us that relation between the two has the form Y=m+X2+c. Available to us are samples of the variables X and Y. Is it possible to apply linear regression to this data to estimate the values of m and c?**

a. no

b. yes

c. insufficient information

**Answer: a. no**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q7. In a binary classification scenario where x is the independent variable and y is the dependent variable, logistic regression assumes that the conditional distribution y|x follows a**

a. Bernoulli distribution

b. binomial distribution

c. normal distribution

d. exponential distribution

**Answer: a. Bernoulli distribution**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q8. Consider the following data:**

**Assuming that you apply LDA to this data, what is the estimated covariance matrix?**

a. [1.8750.31250.31250.9375]

b. [2.50.41670.41671.25]

c. [1.8750.31250.31251.2188]

d. [2.50.41670.41671.625]

e. [3.251.16671.16672.375]

f. [2.43750.8750.8751.7812]

g. None of these

**Answer: g. None of these**

**Q9. Given the following 3D input data, identify the principal component.**

**(Steps: center the data, calculate the sample covariance matrix, calculate the eigenvectors and eigenvalues, identify the principal component)**

a. [−0.1022 0.0018 0.9948]

b. [0.5742 −0.8164 0.0605]

c. [0.5742 0.8164 0.0605]

d. [−0.5742 0.8164 0.0605]

e. [0.8123 0.5774 0.0824]

f. None of the above

**Answer: e. [0.8123 0.5774 0.0824]**

**Q10. For the data given in the previous question, find the transformed input along the first two principal components.**

a.

b.

c.

d.

e. None of the above

**Answer: c**

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**Q1. For linear classification we use:**

a. A linear function to separate the classes.

b. A linear function to model the data.

c. A linear loss.

d. Non-linear function to fit the data.

**Answer: b. A linear function to model the data.**

**Q2. Logit transformation for Pr(X=1) for given data is S=[0,1,1,0,1,0,1]**

a. 3/4

b. 4/3

c. 4/7

d. 3/7

**Answer: c. 4/7**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q3. The output of binary class logistic regression lies in this range.**

a. [−∞,∞]

b. [−1,1]

c. [0,1]

d. [−∞,0]

**Answer: d. [−∞,0]**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q4. If log(1−p(x)1+p(x))=β0+βxlog What is p(x)p(x)?**

**Answer: d.**

**Q5. Logistic regression is robust to outliers. Why?**

a. The squashing of output values between [0, 1] dampens the affect of outliers.

b. Linear models are robust to outliers.

c. The parameters in logistic regression tend to take small values due to the nature of the problem setting and hence outliers get translated to the same range as other samples.

d. The given statement is false.

**Answer: d. The given statement is false.**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q6. Aim of LDA is (multiple options may apply)**

a. Minimize intra-class variability.

b. Maximize intra-class variability.

c. Minimize the distance between the mean of classes

d. Maximize the distance between the mean of classes

**Answer: b. Maximize intra-class variability.**

**Q7. We have two classes in our dataset with mean 0 and 1, and variance 2 and 3.**

a. LDA may be able to classify them perfectly.

b. LDA will definitely be able to classify them perfectly.

c. LDA will definitely NOT be able to classify them perfectly.

d. None of the above.

**Answer: a. LDA may be able to classify them perfectly.**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q8. We have two classes in our dataset with mean 0 and 5, and variance 1 and 2.**

a. LDA may be able to classify them perfectly.

b. LDA will definitely be able to classify them perfectly.

c. LDA will definitely NOT be able to classify them perfectly.

d. None of the above.

**Answer: b. LDA will definitely be able to classify them perfectly.**

**Q9. For the two classes ’+’ and ’-’ shown below.**While performing LDA on it, which line is the most appropriate for projecting data points?

a. Red

b. Orange

c. Blue

d. Green

**Answer: b. Orange**

These are Introduction to Machine Learning Nptel Week 3 Answers

**Q10. LDA assumes that the class data is distributed as:**

a. Poisson

b. Uniform

c. Gaussian

d. LDA makes no such assumption.

**Answer: d. LDA makes no such assumption.**

These are Introduction to Machine Learning Nptel Week 3 Answers