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# Chapter 2. Simple Workflow and Passive Debugging

<feature><title>In This Chapter</title>
• Linear Regression: An Example Problem

• Creating a Command-Line Tool

• Dealing with Build Errors

• Simple Debugging

</feature>

For most of this book, we work on applications that do linear regression, a simple but informative statistic. Suppose that you have a series of data pairs, such as the quarterly sales figures for a particular department, as shown in Table 2.1.

Table 2.1. Quarterly Sales Figures for a Hypothetical Company (millions of dollars)

Quarter

Sales

1

107.5

2

110.3

3

114.5

4

116.0

5

119.3

6

122.4

A regression line is the straight line that passes nearest all the data points (see Figure 2.1). The formula for such a line is y = mx + b, or the sales (y) for a given quarter ...

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