Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

492 Chapter 15 MATLAB

Note that if you substitute the solutionx 1 2,x 2 5, andx 3 4 into each equation, you

find that they satisfy them. That is: 2(2) 5  4 13, 3(2) 2(5)4(4) 32, and

5(2)  5 3(4)17.

15.6 Curve Fitting with MATLAB

In Section 14.8, we discussed the concept of curve fitting. MATLAB offers a variety of curve-

fitting options. We will use Example 14.11 to show how you can also use MATLAB to obtain

an equation that closely fits a set of data points. For Example 14.11 (Revisited), we will use the

command POLYFIT(x, y, n),which determines the coefficients (c 0 ,c 1 ,c 2 , ...,cn) of a

polynomial of ordernthat best fits the data according to:

Example 14. 11 Find the equation that best fits the following set of data points in Table 15.13.

(Revisited) In Section 14.8, plots of data points revealed that the relationship betweenyandxis qua-

dratic (second order polynomial). To obtain the coefficients of the second order polynomial

that best fits the given data, we will type the following sequence of commands. The MATLAB

Command Window for Example 14.11 (Revisited) is shown in Figure 15.27.

>>format compact

>> x=0:0.5:3

>> y = [2 0.75 0 -0.25 0 0.75 2]

>> Coefficients = polyfit(x,y,2)

yc 0 x

n

c 1 x

n 1

c 2 x

n 2

c 3 x

n 3

 p cn

■Figure 15.27 The Command Window for Example 14.11 (Revisited).

TABLE 15.13 A Set

of Data Points for

Example 14.11

(Revisited)

XY

0.00 2.00

0.50 0.75

1.00 0.00

1.50 0.25

2.00 0.00

2.50 0.75

3.00 2.00

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