How do Neural Networks work? And how can they be used to help with COVID-19 pandemic?
During the COVID-19 pandemic, it is important to remember not to panic, but to be precautious and stay safe. Please be sure to wash your hands thoroughly and properly, and practice social distancing at this time. Stay safe we can fight this ❤️
With the global pandemic increasing in scale and spreading quickly, it is very important for us to stay precautious, safe, and healthy. There needs to be an efficient way to make diagnosis times easier for doctors, nurses and medical professionals so that they can focus on treatment immediately, and one certain way is to use neural networks and deep learning to find a solution to this problem for us.
About Neural Nets
A Neural Network, or a Neural “Net”, is a deep learning model which sort of acts like a real biological neural network. It is a system which learns a specific pattern by taking in examples, without being explicitly programmed to achieve the task. To build or implement a neural network through code (for example, Python), there are 4 steps to essentially follow: 1. Set the architecture of the model , 2. Compiling the model, 3. Fitting the model, 4. Predicting with the model.
Before we delve into the four step process, lets take a look at how a neural network looks like: A neural network is composed on neurons (or nodes) and layers.
To the left is a diagram of a neural network. The circles represent the neurons/nodes of the system, where data is stored. And the lines connect one node or neuron to another neuron.
There are different layers of a neural network: the first layer Is the input layer, which takes in the inputs or features from our specific dataset. The next layer or layers (until the last layer) is/are called hidden layer(s), and the last layer is the output layer.
A neural network essentially first takes in all of the inputs, maps them to the neurons in the first layer, and then maps those nodes to the next layer by using something called weights. Each line connecting from one node to another node has a certain weight to it. To calculate the value of the next layer, we multiply every previous node value with their corresponding weight, and sum all of the values from the previous layer. So for example, the value of the next node of the second layer ( shown in the second picture to the left) is essentially a sum of all the products of the previous input values and the weights. The weights symbolize how much importance or influence does a particular feature variable of input have on the entire model.
This computation happens until we reach the output layer, which decides which target the data belongs to (predicting the target for the inputs). The output layer consists of the number of possible targets; for example if we needed to classify whether a digit drawing was 0, 1, 2, 3, 4, 5..9, we would have 10 different options for the output, or 10 nodes in the output layer. The neural network would then make a decision by computing and moving forward through the network.
Forward and Back Propagation
This process is called forward propagation. The neural network makes predictions using the process of forward propagation. It takes in the input feature values as the input layer, maps the target values at the output layer, and performs the computations, until it leads to some output target value. Now, what if the network makes a prediction which is not accurate? What if the prediction the network makes is far from the actual value? This is where we need to update the weights so that the values are more closer and accurate with the actual target values. In order to achieve this, the network goes backwards from the output layer to the previous hidden layer(s) (all the way up to the input layer) and updates the weights using an optimizer so that the next predictions are more accurate.
An optimizer is essentially an algorithm which helps us minimize the error of the predicted vs the actual target value. Every time we train our network, our goal is to minimize the loss so that the neural network can accurately predict the next set of data. When we plot our losses for all possible weights, we have to ensure our loss is at its minimum value. In order to find the minimum value loss, we need to look for the minima of the function, or where the slope is 0. The optimizer updates the weights by using a learning rate, which we use to change the weight accordingly.
Four Step Process
Neural networks can be used to solve many many classification or regression problems such as Image Classification, character recognition, and natural language processing. But how do you implement a neural network to solve a problem? These are the 4 steps:
To build a neural network, we first set the whole architecture or the structure of the neural network. We first import the important libraries we need to build this network. The main library we require is the keras library, which is a neural network library in Python.
In this step, you read in the input training dataset. To do this you use the read_csv function from the pandas library (another library in Python for datasets). We then use the Sequential model API in the keras library to build and instantiate the model. A sequential model is pretty self-explanatory; every layer only has connections to the layer coming after it. To add a layer to the model, you can use the .add(Dense()) to specify the layer. There is something called an activation function, which defines the value of a node given the weights and inputs. The relu activation function states that if the value is positive, it’s just the value, else the value is 0. When we define our first layer, we also need to add our input shape, which represents how many columns or feature inputs the dataset has.
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The next step is to compile the model, where we specify the optimizer. The optimizer modifies the weights as throughout the training process, so that the predictions are closer to the actual target. To compile the model, you need to first specify your optimizer (there are many kinds, for example, Adam optimizer, and the SGD — Stochastic Gradient Descent optimizer) and the loss function (for example MSE — mean squared error). The loss function is a way to calculate the error between the predicted and actual values. For MSE, we basically square all of the errors of the predicted/actual values, and take the average of all of them.
The third step is to fit the model with your dataset!! This is a very fun part: you basically fit the X and y dataset portions (which are the input/features and the targets respectively). This will fit the dataset into the model you have created.
The last step is to predict values for your testing set. This is to test the model’s accuracy with data is hasn’t seen before. To do this, you would:
Deep Learning and COVID-19
Deep Learning algorithms and neural networks can help us detect infections from CT scans, using image classification. This can improve the process of diagnosis, and we can also use machine learning to learn from all sorts of data: whether it be the geographically impact of COVID-19, or other external influences of the virus.
Stay safe, healthy and wish y’all loads of happiness!!!! We got this! ❤️
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