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Jien Weng
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Writing

Blog posts on product work and business systems, alongside technical notes on mathematics, AI, and research. Browse the two collections below.

Blog posts

Product decisions, business systems, and lessons from building things.

Experiences1 min read

A Small Talk About Hackathons

What repeated hackathons taught me about exhaustion, comparison, and taking a proper break.

Experiences1 min read

Dead Internet Theory #1

Why polished posts can feel disconnected from the people behind them.

Experiences2 min read

Building a DeepSeek-R1 Chatbot

A Gradio chatbot experiment with visible intermediate output and the 1.5B distilled DeepSeek-R1 model.

Experiences2 min read

Eco Finance: A PayHack Prototype

A carbon-footprint and financial-literacy prototype built during PayHack 2024 with OpenFinance APIs.

Experiences3 min read

First Physical Hackathon Experience

What I learned from my first physical hackathon at PayHack 2024, where we used OpenFinance APIs to prototype a financial-literacy app.

Technical notes

Mathematical explanations, derivations, and worked examples in AI and research.

Linear regression8 lessons · from fitting a line to statistical testing

Follow the derivations in order. Each lesson builds on the notation and results from the previous one.

  1. Simple Linear RegressionAn introduction to simple linear regression, the OLS method, and deriving the estimators using Sxx and Sxy notation.5 min
  2. Multiple Linear RegressionExtending simple linear regression to multiple predictors using matrix notation and deriving the OLS estimator in matrix form.5 min
  3. Polynomial RegressionUnderstanding polynomial regression as a special case of multiple linear regression, with design matrix construction and overfitting considerations.5 min
  4. CorrelationDefining the Pearson correlation coefficient using Sxx, Syy, Sxy, Sx, and Sy notation, and exploring its properties.4 min
  5. R-squared: SST, SSE, SSR and the Relationship with CorrelationDefining the coefficient of determination from the sum of squares decomposition and proving that R-squared equals the square of the correlation coefficient.7 min
  6. Standard Error in RegressionDeriving the standard errors of the regression coefficients using MSE, Sxx, and the variance-covariance matrix.5 min
  7. Confidence Intervals for Regression CoefficientsConstructing confidence intervals for beta_0, beta_1, and beta_i using the t-distribution and standard errors.5 min
  8. Statistical Testing in RegressionPerforming hypothesis tests on regression coefficients using t-tests, p-values, and the connection to confidence intervals.5 min
Regression5 min read

Statistical Testing in Regression

Performing hypothesis tests on regression coefficients using t-tests, p-values, and the connection to confidence intervals.

Regression5 min read

Standard Error in Regression

Deriving the standard errors of the regression coefficients using MSE, Sxx, and the variance-covariance matrix.

Regression4 min read

Correlation

Defining the Pearson correlation coefficient using Sxx, Syy, Sxy, Sx, and Sy notation, and exploring its properties.

Regression5 min read

Polynomial Regression

Understanding polynomial regression as a special case of multiple linear regression, with design matrix construction and overfitting considerations.

Regression5 min read

Multiple Linear Regression

Extending simple linear regression to multiple predictors using matrix notation and deriving the OLS estimator in matrix form.

Regression5 min read

Simple Linear Regression

An introduction to simple linear regression, the OLS method, and deriving the estimators using Sxx and Sxy notation.