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Linear and Logistic Regression Implementation Questions

Covers the fundamentals and implementation details of linear regression for continuous prediction and logistic regression for binary or multiclass classification. Candidates should understand model formulation, hypothesis functions, and the intuition behind fitting a line or hyperplane for regression and using a sigmoid or softmax function for classification. Include loss functions such as mean squared error for regression and cross entropy loss for classification, optimization methods including gradient descent and variants, regularization techniques, feature engineering and scaling, metrics for evaluation such as mean absolute error and accuracy and area under curve, and hyperparameter selection and validation strategies. Expect discussion of practical implementation using numerical libraries and machine learning toolkits, trade offs and limitations of each approach, numerical stability, and common pitfalls such as underfitting and overfitting.

EasyTechnical
0 practiced
Implement the closed form solution for linear regression (normal equation) in Python using NumPy. The function should accept X of shape (n_samples, n_features) and y of shape (n_samples,), add an intercept column internally, handle singular X^T X by using a pseudo-inverse, and return theta of shape (n_features + 1,). Provide a short example showing input arrays and expected output shape.
MediumTechnical
0 practiced
Discuss the use of polynomial features and interaction terms in linear models: how to generate them, the risk of overfitting as degree increases, computational and memory costs, and strategies to pick degrees and regularization strength. Mention alternatives like splines and kernel methods and when they are preferable.
HardTechnical
0 practiced
Explain how L2 regularization (ridge) affects the bias-variance tradeoff in linear regression. Provide mathematical intuition showing how ridge shrinks coefficients, reduces variance, and may increase bias. Describe how to select regularization strength using cross-validation and pitfalls in high-dimensional small-sample regimes.
HardTechnical
0 practiced
Provide an algorithm and implement in Python an incremental update procedure for ridge regression when a new data point arrives. Use the Sherman-Morrison formula to update the inverse of (X^T X + lambda I) efficiently, discuss numerical stability, and state when a full recomputation is necessary.
EasyTechnical
0 practiced
Explain logistic regression for binary classification in production: give the hypothesis using the sigmoid function, relate coefficients to log-odds and odds ratio, describe decision boundary and thresholding, and explain how softmax generalizes logistic regression to multiclass. Also discuss when logistic regression is an appropriate baseline model.

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