Multiclass SVM Optimization

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Questions and Answers

What is the goal of optimization in the context of machine learning?

  • To reduce a cost function $J(W)$ to optimize some performance measure $P$. (correct)
  • To increase the training error on the data.
  • To maximize a cost function to improve performance.
  • To minimize the performance measure $P$ while ignoring the cost function.

In machine learning, what is the significance of minimizing $J(W)$ with respect to parameter $W$ on training data?

  • It directly optimizes the performance on unseen data.
  • It only focuses on minimizing training error without considering test data.
  • It aims to achieve low error on both training and unseen data. (correct)
  • It ensures the test error is high.

Which of the following is not an assumption typically made in machine learning optimization?

  • The training set and test set are identically distributed.
  • Data samples in each dataset are independent.
  • Data samples are dependent on each other. (correct)
  • Test and Training data are generated by the same probability distribution.

How does altering the capacity of a learning algorithm relate to overfitting and underfitting?

<p>It can control the balance between overfitting and underfitting. (A)</p> Signup and view all the answers

What does 'Underfitting' refer to in the context of machine learning models?

<p>A model that is not able to obtain sufficiently low training error. (A)</p> Signup and view all the answers

What characterizes 'Overfitting' in machine learning models?

<p>The gap between training and test error is too large. (D)</p> Signup and view all the answers

In the context of binary classification, which of the following equations represents Logistic Regression?

<p>$p(y|X;W) = \sigma(W'X)$ (B)</p> Signup and view all the answers

What is the primary role of the Softmax classifier?

<p>To generalize binary logistic classification to multiple classes. (A)</p> Signup and view all the answers

What is the purpose of introducing nonlinearity in neural networks?

<p>To enable the network to learn complex patterns that cannot be captured by linear models. (D)</p> Signup and view all the answers

Which of the following activation functions introduces nonlinearity into a neural network?

<p>A threshold function. (D)</p> Signup and view all the answers

What does the ReLU (Rectified Linear Unit) activation function do?

<p>It outputs the input directly if it is positive; otherwise, it outputs zero. (D)</p> Signup and view all the answers

Match the component to its function in a neuron:

<p>Synapse : point of connection to other neurons (B)</p> Signup and view all the answers

In the context of neural networks, what is a key function of the 'Axon'?

<p>To transmit the output of the neuron. (D)</p> Signup and view all the answers

A perceptron is used to implement a two-input AND function. Given the inputs X1 and X2, which of the following conditions must be met to produce an output of 1?

<p>X1 = 1 and X2 = 1 (D)</p> Signup and view all the answers

In the context of neural networks, what does the expression $f^{(K)}(f^{(K-1)}...(f^{(i)}...(f^{(2)}(f^{(1)}(X)))))$ represent

<p>Feed forward in Neural Network (D)</p> Signup and view all the answers

What is the output of an OR function, given inputs $X_1 = 0$ and $X_2 = 0$?

<p>0 (C)</p> Signup and view all the answers

Considering a threshold function where the output is 1 if $x \geq 0$ and 0 if $x < 0$, what will be the output (y) if the input (x) is -2?

<p>0 (D)</p> Signup and view all the answers

Consider the function $y = max(0, x)$. What is the value of $y$ when $x = -5$?

<p>0 (D)</p> Signup and view all the answers

What is a notable downside of using Stochastic Gradient Descent in optimizing a model?

<p>The noisy update process can make it hard for the algorithm to settle on an error minimum for the model. (C)</p> Signup and view all the answers

Why can frequent updates in Stochastic Gradient Descent be considered both an advantage and a disadvantage?

<p>They provide immediate insight into model performance but are more computationally expensive. (C)</p> Signup and view all the answers

What is a primary benefit of using Batch Gradient Descent over Stochastic Gradient Descent?

<p>More computationally efficient updates. (D)</p> Signup and view all the answers

What is a significant drawback of Batch Gradient Descent?

<p>It requires the entire training dataset to be in memory. (B)</p> Signup and view all the answers

How does Mini-Batch Gradient Descent balance the trade-offs between Stochastic and Batch Gradient Descent?

<p>By processing small batches of training examples in each update. (B)</p> Signup and view all the answers

What is a key disadvantage of using Mini-Batch Gradient Descent?

<p>It requires the configuration of an additional 'mini-batch size' hyperparameter. (D)</p> Signup and view all the answers

Given the function for AND logic: $X_1$ | $X_2$ | y ---|---| 0 | 0 | 0 0 | 1 | 0 1 | 0 | 0 1 | 1 | 1

Which inequality describes the decision boundary implemented by the perceptron?

<p>$X_1 + X_2 - 1.5 = 0$ (C)</p> Signup and view all the answers

The XOR function satisfies what expression?

<p>$X_1 \bigoplus X_2 = ( X_1 + X_2).(\overline{X_1} + \overline{X_2})$ (C)</p> Signup and view all the answers

The XOR function satisfies what table?

$X_1$ $X_2$ $h_1$=$X_1$+$X_2$ $h_2$=$\overline{X_1}$ + $\overline{X_2}$ $h_1$ . $h_2$=X1$\bigoplus$X2
0 0 0 1 0
0 1 1 1 1
1 0 1 1 1
1 1 1 0 0

<p>The table is correct (B)</p> Signup and view all the answers

The XOR problem requires what type of network?

<p>Multilayer network (A)</p> Signup and view all the answers

Considering you have to classify images of cats, dogs, and birds. Which of the below is most appropriate?

<p>Softmax regression (C)</p> Signup and view all the answers

What is true about nonlinearity?

<p>Allows models to capture and model complex dataset relationships. (A)</p> Signup and view all the answers

Which is the best way to prevent underfitting?

<p>Increase Model Complexity (C)</p> Signup and view all the answers

What will be the value of 'y' if $x=5$ in the following function? $y = max(0, x)$

<p>5 (A)</p> Signup and view all the answers

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Flashcards

Optimization in ML

Adjusting parameters to minimize a cost function and optimize a performance metric.

Cost Function Minimization

A cost function, denoted as J(W), is minimized with respect to the parameter W using training data.

Data assumptions for ML

Generated by a probability distribution and these samples are also independent.

Underfitting

Model is too simple to capture data patterns. High bias, low variance.

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Overfitting

Model fits training data too well, poor generalization. Low bias, high variance.

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Controlling Over/Underfitting

Adjusting model capacity can control overfitting and underfitting.

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Linear/Logistic Regression

A linear model for regression or binary classification.

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Linear Regression Formula

f : X -> y, where y is a real number.

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Logistic Regression Formula

p(y|X;W) = σ(W'X), where σ is a sigmoid or logistic non linear function.

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Softmax Classifier

s_yi = f(X_i,W)_yi = W^t x X_i, generalization of binary logistic classifier to multiple classes

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Nonlinearity in ML

Handles data not separable by a linear model through non linearities.

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Linear separability

When data can be split with a straight line

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Threshold Activation

Output is 1 if input >= 0, else 0, non-linear model.

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ReLU (Rectified Linear Unit)

Output is max(0, x). Linear for +ve domain, zero otherwise

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Dendrite

Receives signals from other neurons

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Synapse

Point of connection to other neurons

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Soma

Processes the incoming information

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Axon

Transmits the output of this neuron

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Neuron Function

Neural network component

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Neural Network

Building block consisting of many layers for solving more complex problems

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AND Logic NN

Function that returns 1 only if both inputs are 1 else 0, needs threshold

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OR Logic NN

Function that returns 1 if any of the inputs are 1 else 0, uses threshold

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XOR Function NN

Inputs (x1 XOR x2))

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Multi-Layer Model

Neural Network Function with multiple layers.

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Study Notes

Optimization Lecture 16:

  • Multiclass SVM Loss Function, Optimization, Stochastic Gradient Descent, Batch Optimization, and Mini-Batch Optimization will be covered.
  • The goal is to optimize the Loss Function via: L = 1/N * ∑∑[max(0,W'Xⱼ -W'X(yi) + ∇] + λ∑∑W²
  • Gradient descent is characterized by: W(yi)(k+1) ← (1-η)W(yi)(k) + 1/N ∑∑[Xi|(W'X-W'X(yi) + ∇ > 0)]
  • Global Minima: The absolute lowest point on a loss function.
  • Local Minima: A point on a loss function that is lower than its surrounding points but not the absolute lowest.
  • Stochastic Gradient Descent: Frequent updates occur, giving insight into model performance and improvement rate and it is the simplest to understand and implement.
  • Batch Gradient Descent: Efficient computation makes convergence stable and prediction errors support parallel processing implementations
  • Mini-Batch Gradient Descent: Update frequency is higher than batch-gradient descent which allows for robust convergence with good batching efficiency

Optimization in Machine Learning Lecture 17:

  • Covered topics include optimization, stochastic gradient descent, batch optimization, mini-batch optimization, optimization in ML, linear and logistic regression, softmax classifier, and nonlinearity.
  • The goal of optimization is to reduce a cost function J(W)
  • The performance of ML is its ability to make the training error small and reduce the gap between training and test error.
  • Underfitting refers to a model that cannot obtain sufficiently low training error
  • Overfitting refers to a model where the gap between training and test error is too large.
  • Overfitting/Underfitting can be controlled by altering a model's capacity, giving algorithms selection ability
  • Linear Regression: f : X ∈ Rᵈ → y ∈ R, ŷ = WᵗX
  • Logistic Regression: p( y | X ;W ) = σ(WᵗX )
  • σ(W ᵗX ) = 1 / 1 + e⁻ᵂ'X
  • Generalization of Binary Logistic Classifier to Multiple Classes: s(yi) = f(Xi, W)(yi) = (W *Xi)(yi)= W(yi)ᵗX(i)
  • Softmax Classifier: p(yi|Xi;W) = e^(Syi) / ∑e^(Sj)

Neural Network Lecture 19

  • Covered topics include nonlinearity, neural networks, AND logic, OR logic, XOR logic, feed-forward NN, and back-propagation learning.
  • Neuron: Dendrites receive signals, synapses are points of connection, the soma processes info, and the axon transmits the neuron's output.
  • Threshold: Used to distinguish when x >= 0 or x < 0
  • ReLU: Rectified Linear Unit; y = max(0, x)
  • AND Function: Can be modeled with X1 + X2 −1.5 = 0
  • OR Function: Can be modeled with X1 + X2 − 0.5 = 0

Neural Network II Lecture 20

  • Covered topics include neural networks, AND logic, OR logic, XOR logic, feed-forward NN, and back-propagation learning.
  • XOR Function: Can be expressed as: (X1 ⊕ X2 = (X1 + X2).(X̅1 + X̅2)

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