Podcast
Questions and Answers
If the loss function $L(w, b)$ is convex, what is the likely impact of different initializations of $w$ and $b$ on the final values obtained after gradient descent?
If the loss function $L(w, b)$ is convex, what is the likely impact of different initializations of $w$ and $b$ on the final values obtained after gradient descent?
- Different initializations will always converge to different local minima, resulting in varied $L(w, b)$ values.
- Gradient descent is guaranteed to find the optimal solution, regardless of the initial starting w and b values.
- Different initializations may lead to the same global minimum, resulting in similar $L(w, b)$ values, provided the learning rate is appropriately tuned. (correct)
- Different initializations will cause gradient descent to oscillate indefinitely, preventing convergence to any minimum.
In the gradient descent algorithm, which of the following statements accurately describes the role of the learning rate, denoted as η?
In the gradient descent algorithm, which of the following statements accurately describes the role of the learning rate, denoted as η?
- It determines the magnitude of the update to the weights $w$ and bias $b$ in each iteration; a large learning rate guarantees faster convergence.
- It scales the gradient vector, controlling the step size during updates; an excessively large learning rate can lead to overshooting the minimum. (correct)
- It is a hyperparameter that is automatically adjusted during training to ensure optimal convergence.
- It introduces randomness into the update process, preventing the algorithm from getting stuck in local minima.
Consider a scenario where the partial derivative of the loss function $L$ with respect to weight $w$ (i.e., $\frac{\partial L}{\partial w}$) is consistently positive during multiple iterations of gradient descent. What does this indicate?
Consider a scenario where the partial derivative of the loss function $L$ with respect to weight $w$ (i.e., $\frac{\partial L}{\partial w}$) is consistently positive during multiple iterations of gradient descent. What does this indicate?
- The weight $w$ needs to be increased to further minimize the loss function $L$.
- The learning rate η should be increased to accelerate weight adjustment of $w$.
- The weight $w$ is already at its optimal value, and no further updates are needed.
- The weight $w$ needs to be decreased to further minimize the loss function $L$. (correct)
When updating weights $w$ and bias $b$ using gradient descent, a temporary variable (e.g., temp_w
, temp_b
) is often used. What issue does using temporary variables prevent?
When updating weights $w$ and bias $b$ using gradient descent, a temporary variable (e.g., temp_w
, temp_b
) is often used. What issue does using temporary variables prevent?
Assume you are training a model with a very small learning rate. What is the most likely consequence of this choice?
Assume you are training a model with a very small learning rate. What is the most likely consequence of this choice?
In a multiple linear regression model with K independent variables, how is the predicted value $ŷ$ calculated?
In a multiple linear regression model with K independent variables, how is the predicted value $ŷ$ calculated?
What is the primary objective when adjusting the parameters w
and b
in a linear regression model?
What is the primary objective when adjusting the parameters w
and b
in a linear regression model?
What does the term 'bias' (b
) represent in the context of a linear regression model?
What does the term 'bias' (b
) represent in the context of a linear regression model?
Given a set of training examples $(x_n, y_n)$ from $n=1$ to $N$, and a linear model $ŷ_n = f_{w,b}(x_n) = wx_n + b$, how is the Mean Squared Error (MSE) loss function defined?
Given a set of training examples $(x_n, y_n)$ from $n=1$ to $N$, and a linear model $ŷ_n = f_{w,b}(x_n) = wx_n + b$, how is the Mean Squared Error (MSE) loss function defined?
In the equation $f_{w,b}(x) = 4x_1 - 2x_2 + 4x_3 + 40$, which term represents the bias?
In the equation $f_{w,b}(x) = 4x_1 - 2x_2 + 4x_3 + 40$, which term represents the bias?
Given the linear regression model $ŷ = f_{w,b}(x)$ and the loss function $L(w, b)$, which of the following statements best describes the relationship between them?
Given the linear regression model $ŷ = f_{w,b}(x)$ and the loss function $L(w, b)$, which of the following statements best describes the relationship between them?
What does minimizing the Mean Squared Error (MSE) in linear regression achieve?
What does minimizing the Mean Squared Error (MSE) in linear regression achieve?
In the context of linear regression, what do the 'weights' ($w_1, w_2, ..., w_K$) represent?
In the context of linear regression, what do the 'weights' ($w_1, w_2, ..., w_K$) represent?
In the context of gradient descent, what is the expected behavior of the loss function $L(\vec{w}, b)$ if the algorithm is functioning correctly?
In the context of gradient descent, what is the expected behavior of the loss function $L(\vec{w}, b)$ if the algorithm is functioning correctly?
What criterion can be used to stop the training process when using gradient descent?
What criterion can be used to stop the training process when using gradient descent?
Which of the following statements best describes the difference between model parameters and hyperparameters?
Which of the following statements best describes the difference between model parameters and hyperparameters?
In the gradient descent update rule $w = w - \eta \frac{\partial L}{\partial w}$, if $\frac{\partial L}{\partial w}$ is a negative number, what effect does this have on the value of $w$ in the next iteration, assuming $\eta$ is positive?
In the gradient descent update rule $w = w - \eta \frac{\partial L}{\partial w}$, if $\frac{\partial L}{\partial w}$ is a negative number, what effect does this have on the value of $w$ in the next iteration, assuming $\eta$ is positive?
For a linear regression model $f_{w,b}(x) = wx + b$, which of the following correctly identifies the inputs/features and the parameters that need to be learned during the training stage?
For a linear regression model $f_{w,b}(x) = wx + b$, which of the following correctly identifies the inputs/features and the parameters that need to be learned during the training stage?
In the context of gradient descent for a simple linear regression, what does 'convergence' generally imply?
In the context of gradient descent for a simple linear regression, what does 'convergence' generally imply?
What is the role of the learning rate (η) in the gradient descent algorithm?
What is the role of the learning rate (η) in the gradient descent algorithm?
In linear regression, what does it indicate if you find parameters $w$ and $b$ such that the loss function $L(w, b)$ is very close to 0 on the training dataset?
In linear regression, what does it indicate if you find parameters $w$ and $b$ such that the loss function $L(w, b)$ is very close to 0 on the training dataset?
Given the MSE loss function $L(w, b) = \frac{1}{2N} \sum_{n=1}^{N} (f_{w,b}(x_n) - y_n)^2$, where $f_{w,b}(x) = wx + b$, what does the term $(f_{w,b}(x_n) - y_n)$ represent?
Given the MSE loss function $L(w, b) = \frac{1}{2N} \sum_{n=1}^{N} (f_{w,b}(x_n) - y_n)^2$, where $f_{w,b}(x) = wx + b$, what does the term $(f_{w,b}(x_n) - y_n)$ represent?
Which of the following is an example of a hyperparameter in a machine learning model?
Which of the following is an example of a hyperparameter in a machine learning model?
How does the number of iterations usually vary across different machine learning tasks when using gradient descent?
How does the number of iterations usually vary across different machine learning tasks when using gradient descent?
How does the gradient descent algorithm update the parameter 'b' (the bias) in a linear regression model?
How does the gradient descent algorithm update the parameter 'b' (the bias) in a linear regression model?
Consider a scenario where the loss function $L(w, b)$ is nonconvex. What is a potential issue when using gradient descent to minimize this loss function?
Consider a scenario where the loss function $L(w, b)$ is nonconvex. What is a potential issue when using gradient descent to minimize this loss function?
In the gradient descent update rules, $\frac{\partial L}{\partial w} = \frac{2}{2N} \sum_{n=1}^{N} (wx_n + b - y_n) \cdot x_n$ and $\frac{\partial L}{\partial b} = \frac{2}{2N} \sum_{n=1}^{N} (wx_n + b - y_n)$, what do these equations represent?
In the gradient descent update rules, $\frac{\partial L}{\partial w} = \frac{2}{2N} \sum_{n=1}^{N} (wx_n + b - y_n) \cdot x_n$ and $\frac{\partial L}{\partial b} = \frac{2}{2N} \sum_{n=1}^{N} (wx_n + b - y_n)$, what do these equations represent?
What does the expression wx + b - y
represent in the context of calculating the derivatives for linear regression?
What does the expression wx + b - y
represent in the context of calculating the derivatives for linear regression?
Why is it important to ensure that gradient descent is working correctly during the training of a model?
Why is it important to ensure that gradient descent is working correctly during the training of a model?
Which of the following is most likely to occur if the learning rate (η) is set too high in gradient descent?
Which of the following is most likely to occur if the learning rate (η) is set too high in gradient descent?
What is the significance of the summation symbol $\sum_{n=1}^{N}$ in the equations for calculating the derivatives of the loss function?
What is the significance of the summation symbol $\sum_{n=1}^{N}$ in the equations for calculating the derivatives of the loss function?
What is the primary purpose of applying a sigmoid function on top of a single output in binary classification?
What is the primary purpose of applying a sigmoid function on top of a single output in binary classification?
In the context of binary classification, what does the term 'binary' refer to?
In the context of binary classification, what does the term 'binary' refer to?
In binary classification, a model outputs a value that is then passed through a sigmoid function. What does this transformed value represent?
In binary classification, a model outputs a value that is then passed through a sigmoid function. What does this transformed value represent?
For a binary classification problem, if you have two output nodes, which function is typically applied to the outputs to obtain probabilities?
For a binary classification problem, if you have two output nodes, which function is typically applied to the outputs to obtain probabilities?
What is the interpretation of the output of a softmax function in a classification problem?
What is the interpretation of the output of a softmax function in a classification problem?
How does Binary Cross-Entropy (BCE) loss function differ from Cross-Entropy loss function based on the information provided?
How does Binary Cross-Entropy (BCE) loss function differ from Cross-Entropy loss function based on the information provided?
Consider a scenario where you're building a spam email detector. What would be an appropriate way to assign labels for binary classification?
Consider a scenario where you're building a spam email detector. What would be an appropriate way to assign labels for binary classification?
What is the purpose of the loss function in the context of training a binary classification model?
What is the purpose of the loss function in the context of training a binary classification model?
Which of the following is an appropriate loss function for a binary classification problem using a sigmoid activation function?
Which of the following is an appropriate loss function for a binary classification problem using a sigmoid activation function?
In the context of binary classification, if a model predicts a probability of 0.9 for an instance belonging to the positive class, how should this be interpreted?
In the context of binary classification, if a model predicts a probability of 0.9 for an instance belonging to the positive class, how should this be interpreted?
In logistic regression, what is the purpose of the sigmoid function?
In logistic regression, what is the purpose of the sigmoid function?
Given the logistic regression equation $\hat{y} = f_{\vec{w},b}(\vec{x}) = g(\vec{w} \cdot \vec{x} + b)$, where $g(z) = \frac{1}{1 + e^{-z}}$, what does $\vec{w} \cdot \vec{x} + b$ represent?
Given the logistic regression equation $\hat{y} = f_{\vec{w},b}(\vec{x}) = g(\vec{w} \cdot \vec{x} + b)$, where $g(z) = \frac{1}{1 + e^{-z}}$, what does $\vec{w} \cdot \vec{x} + b$ represent?
In a logistic regression model predicting whether a student will pass (1) or fail (0) an exam, $x_1$ represents study time and $x_2$ represents exam length. If $f_{\vec{w},b}(\vec{x}) = 0.3$, what is the probability that the student will fail?
In a logistic regression model predicting whether a student will pass (1) or fail (0) an exam, $x_1$ represents study time and $x_2$ represents exam length. If $f_{\vec{w},b}(\vec{x}) = 0.3$, what is the probability that the student will fail?
What does a large value of $z$ (where $z = \vec{w} \cdot \vec{x} + b$) imply in the context of a logistic regression model?
What does a large value of $z$ (where $z = \vec{w} \cdot \vec{x} + b$) imply in the context of a logistic regression model?
Why is logistic regression suitable for binary classification problems?
Why is logistic regression suitable for binary classification problems?
In logistic regression, if the weights $\vec{w}$ are [2, -3] for features $x_1$ and $x_2$ respectively, and the bias $b$ is 1, how does increasing $x_2$ while holding $x_1$ constant affect the predicted probability?
In logistic regression, if the weights $\vec{w}$ are [2, -3] for features $x_1$ and $x_2$ respectively, and the bias $b$ is 1, how does increasing $x_2$ while holding $x_1$ constant affect the predicted probability?
Suppose a logistic regression model predicts the probability of a customer clicking on an ad. If, for a given customer, $z = \vec{w} \cdot \vec{x} + b = 0$, what is the predicted probability of the customer clicking on the ad?
Suppose a logistic regression model predicts the probability of a customer clicking on an ad. If, for a given customer, $z = \vec{w} \cdot \vec{x} + b = 0$, what is the predicted probability of the customer clicking on the ad?
What is the range of possible values for the output of a logistic regression model?
What is the range of possible values for the output of a logistic regression model?
In the context of interpreting logistic regression output, what does $P(y=1)$ represent?
In the context of interpreting logistic regression output, what does $P(y=1)$ represent?
If a student increases their study time ($x_1$) and the coefficient $w_1$ associated with study time in a logistic regression model is positive, what is the likely effect on the probability of passing the exam?
If a student increases their study time ($x_1$) and the coefficient $w_1$ associated with study time in a logistic regression model is positive, what is the likely effect on the probability of passing the exam?
Flashcards
fw,b(x)
fw,b(x)
Function representing predictions in a linear model using weights and bias.
Multiple Linear Regression
Multiple Linear Regression
A regression model that includes two or more independent variables.
Weights (w)
Weights (w)
Parameters in linear regression that adjust the contribution of each independent variable.
Bias (b)
Bias (b)
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Mean Square Error (MSE)
Mean Square Error (MSE)
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Loss Function
Loss Function
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Adjust w and b
Adjust w and b
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Objective of Linear Regression
Objective of Linear Regression
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Loss Function (L(w, b))
Loss Function (L(w, b))
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Gradient Descent
Gradient Descent
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Learning Rate (η)
Learning Rate (η)
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Gradient of L (∇L)
Gradient of L (∇L)
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Simultaneous Update
Simultaneous Update
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Convergence
Convergence
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Model Parameters
Model Parameters
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Hyperparameters
Hyperparameters
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Stopping criterion
Stopping criterion
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Iterations
Iterations
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MSE Loss Function
MSE Loss Function
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Derivative
Derivative
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Local Minimum
Local Minimum
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Global Minimum
Global Minimum
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Binary Classification
Binary Classification
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Sigmoid Function
Sigmoid Function
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Binary Cross Entropy (BCE)
Binary Cross Entropy (BCE)
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Softmax Function
Softmax Function
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Softmax Regression
Softmax Regression
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Output Class
Output Class
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Loss Function in Logistic Regression
Loss Function in Logistic Regression
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Optimization Algorithm
Optimization Algorithm
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Categories in Binary Classification
Categories in Binary Classification
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Learning Objectives of Binary Classification
Learning Objectives of Binary Classification
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Logistic Regression
Logistic Regression
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Probability Output
Probability Output
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z = w·x + b
z = w·x + b
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Unbounded Value
Unbounded Value
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Pass Probability (ŷ)
Pass Probability (ŷ)
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Fail Probability
Fail Probability
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Label (y)
Label (y)
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Logistic Function Formula
Logistic Function Formula
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Interpreting Output
Interpreting Output
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Study Notes
Lab Arrangement
-
Lab groups and associated programs are listed, along with days, times, locations, and instructor/TA details
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P5 group has 106 students in year 2 (SE), meets Tuesdays 11am-1pm in E2-07-13, with instructor Rishabh Ranjan and TAs Nabil Zafran and others
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P1 group has 107 students in year 3 (SE), meets Tuesdays 2pm-4pm in E2-07-13, with instructor Zha Wei and TAs Tony and others
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P4 group has 61 BAC + 67 DSC students, meets Tuesdays 4pm-6pm in E2-07-13, with instructor Junhua Liu and others
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P3 group has 118 IS students, meets Thursday 9am-11am in E2-06-18, with instructor Junhua Liu and others
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P2 group has 31 IS + 86 AAI students (117 total), meets Thursday 11am-1pm in E2-07-13, with instructor Xiaoxiao Miao and TA Ridwan
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Combined lab sessions for P1-P5 are offered online on Wednesday 9am-11am and marked as W12, W13
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Some weeks, (W4, W6, W11), there are no lab sessions
January 19th Instructions
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Students need to complete grouping tasks and submit by January 19th
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Students should post questions related to the project in the group discussion forum
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Lab 1 assignment is expected
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Instructors have provided sample projects for students
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The lab this week is a practice lab and no submission is required
Lecture 2 Topics
- The lecture covers linear regression and practical tips on binary classification
Supervised Learning Tasks
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Regression tasks predict a numerical value (e.g., price prediction, sale prediction) with infinitely many possible outputs
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Classification tasks predict categories (e.g., whether a patient is healthy or not) with a limited number of outputs.
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Linear regression, neural networks, decision trees, random forests, Adaboost, and support vector machines (SVMs) are examples of regression models used for supervised learning tasks
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Logistic regression, neural networks, decision trees, random forests, Adaboost, SVMs, and K-Nearest Neighbors (KNN) and Naive Bayes are examples of classification models used for supervised learning tasks
Simple Linear Regression
-
Simple linear regression involves one independent variable and a dependent variable, modeled linearly
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Learnable parameters are weights (w) and bias (b)
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The formula for predicting a score (ŷ) is f(x) = wx + b, where x is the independent variable, w is the weight, and b is the bias
Multiple Linear Regression
-
Involves two or more independent variables
-
The formula for predicting score (ŷ) is f(x) = w1x1 + w2x2 + ... + wkxk + b, where w1, w2,... wk are weights for each independent variable, x1, x2,... xk are variables, and b is bias.
Loss Function for Linear Regression
-
The objective is to minimize the loss function, which measures the difference between predicted values (ŷ) and true values (y).
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Loss function example: MSE (mean square error) = 1 / (2N) * Σ(ŷn – yn)^2
Gradient Descent Algorithm
-
The algorithm iteratively adjusts parameters (weights and bias) to minimize the loss function.
-
Parameter updates are made in the direction of the negative gradient, often with a learning rate η.
Simple Linear Regression - Gradient Descent Algorithm
- Iterates until convergence {w = w - η*(dL/dw), b = b - η*(dL/db)}, where (dL/dw) and (dL/db) represent the derivative of the loss with respect to weight w and bias b
Derivatives for Linear Regression
- The derivatives of the loss function with respect to w and b are provided.
General Loss Function
-
Nonconvex loss functions can lead to local minimum
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Gradient descent algorithm may stop at a local minimum, not necessarily a global minimum
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Empirical evidence suggests GD works well.
Practical tips for Linear Regression
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Convert data inputs and outputs to numerical values/ format
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Important Hyperparameters: Number of iterations
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Learning rate
Feature Scaling Techniques
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Feature scaling (normalization) aims to place all features in similar ranges, often necessary for the algorithm's effectiveness
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Mean normalization, Max-min normalization, z-score normalization
Binary Classification
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A classification task with two output categories
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Examples include spam/not spam, healthy/unhealthy
Logistic Regression
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Output probability of belonging to a category (e.g., fail or pass)
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Sigmoid function maps output to a value between 0 and 1.
Loss Function for Logistic Regression
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Mean Square Error (MSE) is not suitable for logistic regression; it yields a non-convex loss function, leading to difficulties.
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Binary Cross Entropy (BCE) is preferred in binary classification tasks
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BCE is a convex loss function
Gradient Descent Algorithm for Binary Classification
- Apply the same gradient descent algorithm as for linear regression, changing the loss function to use BCE.
Parameters and Hyperparameters
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Model parameters can be initialized and updated during data learning.
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Hyperparameters (e.g., number of iterations, learning rate) must be set prior to learning.
Case Study
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Input vector x comprises data features (features are fed into the model)
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Model predicts to which category x belongs, output is class y
Interpretation of Logistic Regression Output
- An output z is generated from inputs, converted to a probabilistic value using the sigmoid.
Decision Boundaries for Logistic Regression
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A decision boundary categorizes points based on the output z's sign and their prediction category.
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If the calculated z ≥ 0, prediction y=1 and otherwise y=0, and z = 0 represents the boundary between these predictions
Important Concepts
- This document covers supervised learning, specifically topics like linear regression and binary classification. Key concepts include model parameters, hyperparameters, loss functions (like MSE and BCE), gradient descent algorithms for optimization, and techniques for input (feature) scaling when using ML models. Different normalization (scaling) methods are examined, such as mean normalization, z-score normalization, and max-min scaling. Information on setting up data for machine learning models and assessing the efficacy of results using appropriate loss functions is covered.
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Description
This quiz covers key aspects of gradient descent, including the impact of initialization, the role of the learning rate, and the use of temporary variables. It also addresses the consequences of using a small learning rate and the calculation of predicted values in multiple linear regression.