# Machine Learning/AI Algorithms Coded From Scratch

Coding machine learning and artificial intelligence algorithms from scratch shows a deep understanding of the algorithms and how they work. The following list of algorithms link to code in an ML/AI GitHub Repository containing the algorithms Barrett Duna wrote.

These algorithms were written in Python 3 from scratch by Barrett Duna. The two main packages they make use of are pandas and numpy. Pandas is a data frame package for loading, describing and manipulating data frames. Numpy is a scientific numeric computing package that works on arrays of all dimensions.

• Perceptron
• This is the original single-layer artificial neural network. It's very simple which applies a simple step function and updates the weights proportional to the error between the predicted output and the actual output.
• This is a later (in history) modification to the simple perceptron. Instead of applying the step function before training, Adaline applies the weight update step before the step function as compared to Adaline.
• K Nearest Neighbors (KNN)
• This algorithm classifies new data points based on the K closest neighbors as measured by the euclidean distance. For a prediction, each distance is calculated between the new data point and the data points in the dataset and the K closest data points vote on the class. • Linear Regression with Stochastic Gradient Descent
• This is an implementation of multivariate linear regression using stochastic gradient descent (SGD) to train the model. SGD, as opposed to batch gradient descent or mini-batch gradient descent, updates the weights of the linear regression model one data point at a time.  One challenge was getting the model to converge to a solution. The challenge was overcome by standardizing the feature inputs in the fitting process and then unstandardizing them before output.
• Logistic Regression
• Logistic regression uses a sigmoid activation function to squash weighted inputs into probabilities between zero and one.  This allows binary classification because you can compare the probability of class 1 to class 0 and choose the class with the highest probability.
• K-Means Clustering Algorithm
• This algorithm differs from the others because it is an unsupervised clustering algorithm as compared to the supervised algorithms above. It randomly chooses K points and iterates over the dataset and assigns each point to one of K clusters based on the closest distance. It then computes the average of the new clusters (called the clusters' centroids) and repeats the process until the centroids remain unchanged.   For some interesting projects I've done check out my ML/AI Projects page.