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- COMP-551 : Applied Machine Learning Programming Assignment #2

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Linear Classification and Nearest Neighbor Classification

1. You will use a synthetic data set for the classification task that you’ll generate yourself.

Generate two classes with 20 features each. Each class is given by a multivariate Gaussian

distribution, with both classes sharing the same covariance matrix. You are provided

with the mean vectors (DS1-m0 for mean vector of negative class and DS1-m1 for mean

vector of positive class) and the covariance matrix (DS1-cov). Generate 2000 examples

for each class, and label the data to be positive if they came from the Gaussian with

mean m1 and negative if they came from the Gaussian with mean m0. Randomly pick

30% of each class (i.e., 600 data points per class) as a test set, and train the classifiers

on the remaining 70%. data When you report performance results, it should be on the

left out 30%. Call this dataset at DS1, and submit it with your code.

2. We first consider the probabilistic LDA model as seen in class: given the class variable,

the data are assumed to be Gaussians with different means for different classes but with

the same covariance matrix. This model can formally be specified as follows:

Y ∼ Bernoulli(π), X | Y = j ∼ N (µj

, Σ).

Estimate the parameters of the probabilistic LDA model using the maximum likelihood

approach. For DS1, report the best fit accuracy, precision, recall and F-measure achieved

by the classifier, along with the coefficients learnt.

3. For DS1, use k-NN to learn a classifier. Repeat the experiment for different values of k

and report the performance for each value. We will compare this non-linear classifier to

the linear approach, and find out how powerful linear classifiers can be. Do you do better

than LDA or worse? Are there particular values of k which perform better? Report the

best fit accuracy, precision, recall and f-measure achieved by this classifier.

4. Now instead of having a single multivariate Gaussian distribution per class, each class

is going to be generated by a mixture of 3 Gaussians. For each class, we’ll define

3 Gaussians, with the first Gaussian of the first class sharing the covariance matrix

with the first Gaussian of the second class and so on. For both the classes, fix the

mixture probability as (0.1,0.42,0.48) i.e. the sample has arisen from first Gaussian with

probability 0.1, second with probability 0.42 and so on. Mean for three Gaussians in the

positive class are given as DS2-c1-m1, DS2-c1-m2, DS2-c1-m3. Mean for three Gaussians

in the negative class are gives as DS2-c2-m1, DS2-c2-m2, DS2-c2-m3. Corresponding 3

covariance matrices are given as DS2-cov-1, DS2-cov-2 and DS2-cov-3. Now sample from

this distribution and generate the dataset similar to question 1. Call this dataset as DS2,

and submit it with your code.

5. Now perform the experiments in questions 2 and 3 again, but now using DS2. Report

the same performance measures as before. What do you observe?

6. Comment on any similarities and differences between the performance of both classifiers

on datasets DS1 and DS2?

Instruction for code submission

1. Submit a single zipped folder with your McGill id as the name of the folder. For

example if your McGill ID is 12345678, then the submission should be 12345678.zip.

2. If you are using python, you must submit your solution as a jupyter notebook.

3. Make sure all the data files needed to run your code is within the folder and loaded with

relative path. We should be able to run your code without making any modifications.

Instruction for report submission

1. You report should be brief and to the point. When asked for comments, your comment

should not be more than 3-4 lines.

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2. Do not include your code in the report!

3. If you report consists of more than one page, make sure the pages are stapled.

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