๐ From Trendlines to Truth: Least Squares Meets Real-World Data (with SageMath!)
How do we find the “best fit” line or curve through scattered data points? Whether you're analyzing athlete performance, plant growth, or social media engagement, least squares fitting provides a powerful, calculus-driven solution.
Let’s dive into how local minima help us find the optimal line or curve, and how SageMath makes it visually and interactively clear.
๐งฎ Problem Setup: What Are We Minimizing?
We’re trying to fit a model (like a line or a parabola) to a collection of data points (xi, yi), minimizing the sum of squared errors between the actual and predicted values.
- Linear Fit: y = mx + c
The error function is defined as:
\[ f(m,c) = \sum_{i=1}^{n} (y_i - mx_i - c)^2 \]
- Parabolic Fit: y = ax2 + bx + c
The error function is defined as:
\[ f(a,b,c) = \sum_{i=1}^{n} (y_i - ax_i^2 - bx_i - c)^2 \]
๐ Try It Yourself! Fit a Line to Data
๐ Visualizing the Best-Fit Line
๐ Now Fit a Parabola
๐ Side-by-Side Comparison
๐ง Observation Prompt:
Which fit better matches the data? When does the curve improve accuracy—and when might it overcomplicate things?
๐ง Your Turn: Data Detective!
- Step 1: Choose your own dataset (sports scores, plant height, stock trend, etc.)
- Step 2: Use the SageMath code to fit a line and parabola
- Step 3: Plot and compare the fits visually + compute sum of squared errors
- Step 4: Analyze:
- Which model fits your data better visually?
- Which one gives a smaller error?
- Why might one model be more appropriate?
๐ฌ Share your work in the comments! Let us know what data you used, your insights, and even your plots or Sage code!
๐ Real-World Examples of Least Squares
| Domain |
Application |
| ๐ฑ Agriculture : |
Predicting plant growth over time |
| ๐ Sports : |
Estimating an athlete’s training progression |
| ๐ Finance : |
Smoothing trends in stock prices |
| ๐ฃ Marketing : |
Modeling customer response to ad exposure |
⚠️ Model Limitations: Don't Just Trust the Fit!
- Overfitting: A parabola might match noise, not signal.
- Underfitting: A line might miss curvature in the trend.
- Assumptions: Least squares assumes error is symmetric and data is real-valued.
๐ง Think Deeper
- When might a linear model be good enough, even for curved data?
- Where could a parabolic model mislead us?
- What if the true model isn’t linear or parabolic—how can we tell?
๐ฎ What’s Next?
We’ve tackled fitting lines and curves in 2D — but what if your data lives in 3D?
Up next:
๐ Fitting a Plane in Space
We’ll learn how to fit a plane of the form
\[ z = ax + by + c \]
to a scattered set of 3D data points using least squares minimization — just like before, but now with partial derivatives in play!
You'll discover how this applies to:
- ๐ Predicting values in multivariable datasets
- ๐ Creating smoother surfaces from scattered terrain data
- ๐ง Modeling decision boundaries in machine learning
And that’s just the beginning...
๐ง Also Coming Soon:
- ๐งฎ Residual Analysis & R²: How good is your model?
- ๐ Model Selection: Linear vs Parabolic vs Exponential
- ๐ Error Surfaces and Gradient Descent Visualized
- ๐งฌ Real-World Case Studies (from biology, marketing, and physics!)
➡️ Subscribe or bookmark to get notified — you won’t want to miss the leap into higher dimensions!
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