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COMP551-Assignment 2 Linear Classification and Nearest Neighbor Classification Solved
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 di↵erent means for di↵erent classes but with the same covariance matrix. This model can formally be specified as follows:
Y ⇠ Bernoulli(⇡), X |Y = j ⇠ N(µj,⌃).
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 coe cients learnt.
3. For DS1, use k-NN to learn a classifier. Repeat the experiment for di↵erent 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 classis 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. Reportthe same performance measures as before. What do you observe?
6. Comment on any similarities and di↵erences between the performance of both classifiers on datasets DS1 and DS2?
2. We first consider the probabilistic LDA model as seen in class: given the class variable,the data are assumed to be Gaussians with di↵erent means for di↵erent classes but with the same covariance matrix. This model can formally be specified as follows:
Y ⇠ Bernoulli(⇡), X |Y = j ⇠ N(µj,⌃).
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 coe cients learnt.
3. For DS1, use k-NN to learn a classifier. Repeat the experiment for di↵erent 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 classis 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. Reportthe same performance measures as before. What do you observe?
6. Comment on any similarities and di↵erences between the performance of both classifiers on datasets DS1 and DS2?
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