Assignment 3: Multi-layer Perceptrons Solution

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This assignment is designed to provide you with rst-hand experience on how TensorFlow works. We will continue on from assignment 2, and this time use TensorFlow to implement a classi er using the Multi-layer Perceptron.

  • Instructions

1.1 Submission package

Within the homework assignment package, there should be a, which contains the directory structure and empty les for you to get started. Please edit the contents within the le for code, and then create a zip archive with the le name, and submit it. Do not use other archive formats such as rar or tar.gz. Also, submit the report in pdf, as a separate le alongside the archive with the codes.

All assignments should be submitted electronically. Hand written reports are not ac-cepted. You can, however, include scanned pages in your report. For example, if you are not comfortable with writing equations, you can include a scanned copy.

1.2 Assignment Report

Even for programming assignments, all results should be summarised in a assignment report. Reports should be in pdf format. Though not mandatory, students are encouraged to submit their reports written in LATEX. In the assignment package, you should have been given an empty skeleton le for you to get started.

However, it is not required for you to explain your code in the reports. Reports are for discussing results. You should however, provide comments in your code, well enough to be understood by directly reading the code.

1.3 Code

All assignments should be in Python 3. Codes that fail to run on Python 3 will receive 20% deduction on the nal score. In other words, do not use Python 2.7.

For this assignment, you should not need to create additional les. Fill in the skeleton les in the submission package. Do not change the name of these scripts.

It is strongly encouraged to follow PEP8. It makes your code much more readable, and less room for mistakes. There are many open source tools available to automatically do this for you.

1.4 Delayed submission

In case you think you will not meet the deadline due to network speed or any other reasons, you can send an email with the SHA-256 hash of your .zip archive rst, and then submit your assignment through email later on. This will not be considered as a delay.

Delayed submissions are subject to 20% degradation per day. For example, an assignment submitted 1 minute after the deadline will receive 80% of the entire mark, even if it was perfect. Likewise, an assignment that was submitted one day and 1 minute after the deadline will receive 60%.

1.5 Use of open source code

Any library under any type of open source license is allowed for use, given full attribution. This attribution should include the name of the original author, the source from which the code was obtained, and indicate terms of the license. Note that using copyrighted material without an appropriate license is not permitted. Short snippets of code on public websites such as StackOver ow may be used without an explicit license, but proper attribution should be given even in such case. This means that if you embed a snippet into your own code, you should properly cite it through the comments, and also embed the full citation in a LICENSES le. However, if you include a full, unmodi ed source, which already contains the license within the source le, this is unnecessary. Please note that without proper attribution, it will be considered plagiarism.

In addition, as the assignments are intended for you to learn, (1) if the external code implements the core objective of the task, no points will be given; (2) code from other CSC486B/CSC586B students will count as plagiarism. To be more clear on (1), with the assignment, we will release a requirements.txt le, that you can use with pip to setup your environment. On top, you are also allowed to use OpenCV3.X, which we will not include in requirements.txt as OpenCV installation depends on your own framework.

2 Continuation from assignment 2

This assignment is a continuation from the second assignment. However, do not worry as the parts that were necessary for you to implement in the second assignment is already done for you in the assignment package.

However, in this assignment, we will not implement cross-validation, but rather will rely on simply a random split of the training set to 80% being the training set, and 20% being the validation set. Again you will need to test on the test set to report your nal performance.

Another thing we will be doing is that we will implement our function as a Python class. This makes it much easier to re-use the model for both training and testing. This is because we construct the computational graph when the class is initialized, and use it for both training and testing.

  • Implementing MyNetwork (80 points)

In this assignment, we are going to implement our network as a Python Class object. The rea-son we want to do this is because of how TensorFlow operates. Remember that in TensorFlow we rst declare our computation graph rst, set everything up, and then run it. If you think about it, it nicely ts into the concept of object oriented programming. You initialize your object, then use class attributes to store things (e.g. your computation graph, placeholders to be used later, etc.), and execute things through class methods. This is what we will do.

Functions that could be used to implement your assignments are embedded in the comments! They may not be the complete set, but should de nitely help!

3.1 build placeholder (0 points)

A function that creates the placeholders for data input. This part is already done for you, but do take a look.

3.2 build preprocessing (5 points)

Implement a function that creates the placeholders for reading and storing the training dataset’s mean and range, and then create an TensorFlow operation that executes that assignment.

3.3 build model (15 points)

Implement the function to build your multi-layer perceptron. Allow the network generation to take con guration parameters such as the number of neurons in a layer, and the number of hidden layers. Also allow the con guration to decide which activation function you want to apply.

Optional: Try using batch normalization before the activation. This is purely optional, and there will not be additional points for this. However, it’s just fun to play around with deep nets.

3.4 build loss (5 points)

Implement the loss function. We will stick to cross entropy this time.

3.5 build optim (10 points)

Implement the optimizer using Adam.

Optional: If you are using batch normalization, make sure that you are using control dependencies. See this link for more details.

3.6 build eval (5 points)

Implement the evaluation related TensorFlow operations. We will also create a summary at this point to see this through TensorBoard.

3.7 build summary (0 points)

This part has been done for you. We will simply gather all summary ops and create a single self.summary op that we use later.

3.8 build writer (5 points)

Implement a function that creates summary writers and TensorFlow saver instances.

3.9 train (25 points)

We will reuse a lot from our previous assignment. Implement according to the comments in the assignment package.

3.10 test (10 points)

Implement the test function. You will need to load the best model you obtained through validation. Implement according to the comments.

  • Reporting (20 points)

As our nal goal is to analyze the results we get, reporting is also a critical element. For this assignment, you will have to report the following mandatory items.

Note that we are now going to use TensorBoard for graph illustrations. You can draw mul-tiple lines in the same graph by designating sub directories in a proper way. Do this to draw multiple experiments on the same graph when you are comparing di erent con gurations.

4.1 Abstract (5 points)

Write a brief abstract summarizing the assignment, as well as your discoveries.

4.2 Activation functions (10 points)

Discuss your ndings about how the convergence changes when you modify your activation function. Also discuss how the accuracy changes. When discussing, use the graphs you obtained through TensorBoard. You are required to compare tanh and relu for a single hyperparameter setting as minimum. You are free to do more if you want.

4.3 Network Architectures (5 points)

Also discuss how your network behaves according the di erent architectures that you have tried. If implemented correctly, you can easily alter the architecture with con gurations. You are required to try minimum of two architectural choices with the same hyperparameter setting. You are free to do more if you want.