 f(x_1, x_2, x_3, ... x_N) $$

But some big questions remain:
- What are all these inputs `\(x_1, x_2, ...\)`?
- What is the functional form? (How does the box work?)

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# The Data Generating Process

For some questions, the set of inputs and their functional form are discoverable.

**Physics example:** How long does it take for an object to fall from a particular height?

$$ t = \sqrt{2h/g} \approx 0.452 \sqrt{h}  $$

Newton and others did experiments to learn the functional form.

&lt;img src="img/blac