R语言: 潜在变量和神经网络

Assignment 2
Latent Variables and Neural Networks
Due Date: 21:59:59 18 October 2019
Please note that,
1. 1 sec delay will be penalized as 1-3 days delay. So please submit your
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2. We will not accept any resubmit version. So please double check your
assignment before the submission.
This assignment consists of three parts (A,B,C), which cover latent variables models and
neural networks (Modules 4 and 5). The total marks of this assessment is 100 and will
contribute 16% to your final score.
Part A. Document Clustering
In this part, you solve a document clustering problem using unsupervised learning algorithms
(i.e., soft and hard Expectation Maximization) for document clustering.
Question 1 [EM for Document Clustering, 40 Marks]
I. Derive Expectation and Maximization steps of the hard-EM algorithm for Document
Clustering, show your work in your submitted PDF report. In particular, include all model
parameters that should be learnt and the exact expression (using the same math
convention that we saw in the Module 4) that should be used to update these
parameters during the learning process (ie., E step, M step and assignments).
II. Implement the hard-EM (you derived above) and soft-EM (derived in Chapter 5 of
Module 4). Please provide enough comments in your submitted code.
Hint. If it helps, feel free to base your code on the provided code for EM algorithm
for GMM in Activity 4.1 or the codebase provided in the Moodle).
III. Load Task2A.text file and necessary libraries (if needed, perform text preprocessing
similar to what we did in Activity 4.2), set the number of clusters K=4, and run both
the soft-EM and hard-EM algorithms on the provided data.
IV. Perform a PCA on the clusterings that you get based on the hard-EM and soft-EM in
the same way we did in Activity 4.2. Then, visualize the obtained clusters with
different colors where x and y axes are the first two principal components (similar to
Activity 4.2). Save your visualizations as plots, and attach them to your PDF report.
Part B. Neural Network vs. Perceptron
In this part, you apply a 3-layer Neural Network on a synthetically generated data to
compare its performance with Perceptron. Here, we are looking for your explanation about
the differences between perceptron and NN that leads to different results.
Question 2 [Neural Network’s Decision Boundary, 30 Marks]
I. Load Task2B_train.csv and Task2B_test.csv sets, plot the training data with
classes are marked with different colors, and attach the plot to your PDF report.
II. Run the implementations of Perceptron given to you in Activity 3.1, calculate the test
error, and plot the test data while the points are colored with their estimated class
labels; attach the plot to your PDF report.
Hint. Note that you must remove NA records from the datasets (using
“complete.cases()’ function). You may also choose to change the labels from [0, 1] to
[-1, +1] for your convenience. If you decided to use the code from Activity 3.1, you
may need to change some initial settings (e.g., epsilon and tau.max). Finally,
remember that perceptron is sensitive to initial weights. Therefore, we recommend to
run your code a few times with different initial weights.
III. Run the 3-layer Neural Network given to you in Activity 5.1 with different values of K
(i.e, number of units in the hidden layer) and record testing error for each of them;
plot the error vs K and attach it to your PDF report. Based on this plot, find the best K and
the corresponding model, then plot the test data while the points are colored with
their estimated class labels using the best model that you have selected; attach the
plot to your PDF report.
Hint. In case you choose to use the provided examples in Activity 5.1, you may need
to transpose the dataset ()using “t()” function) and use different values for parameter
settings (e.g., lambda). We also recommend to change K to 2, 4, 6, .., 100 (i.e. from
2 to 100 with the step size of 2).
IV. In a table, report the error rates obtained by the perceptron and all variants of NN.
Then bold the best model (with minimum error). Add this table to your PDF report.
V. In your PDF report explain the reason(s) responsible for such difference between
perceptron and a 3-layer NN.
Hint: Look at the plots and think about the model assumptions.
Part C. Self-Taught Learning
In this part, you implement self-taught learning for Neural Network using the Autoencoder
that provided in Activity 5.2 and a 3-layer NN (from Activity 5.1 or H2O package)
Question 3 [Self Taught Neural Network Learning, 30 Marks]
I. Load Task2C_labeled.csv, Task2C_unlabeled.csv and Task2C_test.csv data
sets and required libraries (e.g., H2O). Note that we are going to use
Task2C_labeled.csv and Task2C_unlabeled.csv for training the autoencoder. We
are going to use Task2C_labeled.csv for training the classifier. Finally, we evaluate
the trained classifier on the test Task2C_test.csv.
II. Train an autoencoder (similar to Activity 5.2) with only one hidden layer and change
the number of its neurons to: 20, 40, 60, 80, .., 500 (i.e. from 20 to 500 with a step
size of 20).
III. For each model in Step II, calculate and record the reconstruction error which is
simply the average (over all data points while the model is fixed) of Euclidian
distances between the input and output of the autoencoder (you can simply use
“h2o.anomaly()” function). Plot these values where the x-axis is the number of units
in the middle layer and the y-axis is the reconstruction error. Then, save and attach
the plot to your PDF report. Explain your findings based on the plot in your PDF report.
IV. Use the 3-layer NN from Activity 5.1 or “h2o.deeplearning” function (make sure you
set “ autoencoder = FALSE”) to build a classification model with 100 units in the
hidden layer using all the original attributes from the training set. Then, calculate and
record the test error.
V. Build augmented self-taught networks using the models learnt in Step II. For each
A. Add the output of the middle layer as extra features to the original feature set,
B. Train a 3-layer NN (similar to Step IV) using all features (original + extra).
Then calculate and record the test error.
VI. Plot the error rates for the 3-layer neural networks from Step V while the x-axis is
the number of extra features and y-axis is the classification error. Save and attach
the plot to your PDF report.
VII. Report the optimum number(s) of units in the middle layer of the autoencoder in
terms of the reconstruction and misclassification errors.
VIII. Comparing the plot from Step III and VI, do you observe any relation between the
reconstruction error and misclassification error? Explain your finding and add them to
your PDF report.
Hint. Since the dataset for this task is large and high-dimensional, running the whole
experiments several times is very time consuming. Therefore, it is recommended to only use
a small portion of your data when you develop or debug your code.
Hint. If you can combine Step II and V (so learn each autoencoder only once), you may save
a great portion of the execution time.
Hint. If you don’t see the expected behaviour in your plots, you may need to check that the
data is clean, i.e. it doesn;t have NA entries, it’s normalised etc. Moreover, you may need to
check that your implementation of the model and training/decoding algorithms is correct.
Submission & Due Date:
The files that you need to submit are:
1. Jupyter Notebook files containing the code for questions {1,2,3} with the extension
“.ipynb”. The file names should be in the following format:
where ‘X=1,2,3’ is the question number. For example, the Notebook for Question 2
Should be named STUDNETID_assessment_2_q2.ipynb
2. You must add enough comments to your code to make it readable and
understandable by the tutor. Furthermore, you may be asked to meet (online) with
your tutor when your assessment is marked to complete your interview.
3. A PDF file that contains your report, the file name should be in the following format:
You should replace STUDENTID with your own student ID. All files must be submitted via
Assessment Criteria:
The following outlines the criteria which you will be assessed against:
● Ability to understand the fundamentals of neural networks and latent variable models.
● Working code: The code executes without errors and produces correct results.
● Quality of report: You report should show your understanding of the latent variable
models and neural networks by answering the questions in this assessment and
attaching the required figures.
● Late submission (-20% of awarded marks for between 1-3 days late, -50% for
between 4-6 days late. 0 marks awards after 6 days)
● Jupyter Notebook file is not properly named (-5%)
● The report PDF file is not properly named (-5%)

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