
Concept explainers
Recompute the regression fits from Probs. (a) 17.3 and (b) 17.17, using the matrix approach. Estimate the standard errors and develop 90% confidence intervals for the coefficients.
(a)

To calculate: The coefficient of the regression fit equation of the given databy the use of matrix approach and then calculate standard error and 90% confidence levels for the coefficient.
x | 0 | 2 | 4 | 6 | 9 | 11 | 12 | 15 | 17 | 19 |
y | 5 | 6 | 7 | 6 | 9 | 8 | 7 | 10 | 12 | 12 |
Answer to Problem 22P
Solution:
The value of coefficient by the use of matrix approach is 4.8515 and 0.35247, the standard error for the coefficient is 1.065 and 90% confidence levels for the coefficient a0 and a1 is,
[3.6951, 6.0080] and [0.2501, 0.4548]
Explanation of Solution
Given Information:
The data is,
x | 0 | 2 | 4 | 6 | 9 | 11 | 12 | 15 | 17 | 19 |
y | 5 | 6 | 7 | 6 | 9 | 8 | 7 | 10 | 12 | 12 |
Calculation:
The coefficient of the regression fit equation can be found out by the Matrix approach by following the below steps,
Step 1. First make Z matrix that contain column of ones in the first column and in the second column x value is shown.
Step 2. Now the coefficient of normal equation is made.
Step 3. Now compute the normal equation of the right hand side that is y data.
Step 4. The coefficient of the model can be found out by taking inverse of the result obtained in step 2 and step 3.
The following MATLAB will perform the desired steps,
On the command window, write this command as,
Now, the coefficient of normal equation is calculated as,
Now, the normal equation of y is calculated as,
Finally, the coefficient of the model can be found out,
Therefore, the value of coefficientis 4.8515 and 0.35247.
Now, for calculating the standard error follow these commands,
Now calculate r2 value,
The standard error of the given data is 1.065.
Now for calculating 90% confidence levels for the coefficient, first calculate the inverse of [Z]T[Z] as,
Then the standard error of each coefficient,
Thevalue of TINV(0.1,10−2)=TINV(0.1,8)=1.8595 is determined by the statistic t value calculator. Therefore, the 90% confidence levels for the coefficient is,
Hence, the 90% confidence levels for the coefficient a0 and a1 is [3.6951, 6.0080] and [0.2501, 0.4548] respectively.
(b)

To calculate: The coefficient of the regression fit cubic equation of the given databy the use of matrix approach and then calculate standard error and 90% confidence levels for the coefficient.
x | 3 | 4 | 5 | 7 | 8 | 9 | 11 | 12 |
y | 1.6 | 3.6 | 4.4 | 3.4 | 2.2 | 2.8 | 3.8 | 4.6 |
Answer to Problem 22P
Solution:
The value of coefficient by the use of matrix approach is −11.4887, 7.1438, −1.0412 and 0.0467, the standard error for the coefficient is 0.57 and 90% confidence levels for the coefficient a0,a1,a2 and a3 is,
[−20.0253,−2.9521], [3.0378,11.2498],[−1.6302,−0.4522] and[0.0208, 0.0726].
Explanation of Solution
Given Information:
The data is,
x | 3 | 4 | 5 | 7 | 8 | 9 | 11 | 12 |
y | 1.6 | 3.6 | 4.4 | 3.4 | 2.2 | 2.8 | 3.8 | 4.6 |
Calculation:
The coefficient of the regression fit equation can be found out by the Matrix approach by following the below steps,
Step 1. First make Z matrix that contain column of ones in the first column and in the second column x value is shown.
Step 2. Now the coefficient of normal equation is made.
Step 3. Now compute the normal equation of the right hand side that is y data.
Step 4. The coefficient of the model can be found out by taking inverse of the result obtained in step 2 and step 3.
The following MATLAB will perform the desired steps,
On the command window, write this commandfor cubic equation as,
Now, the coefficient of normal equation is calculated as,
Now, the normal equation of y is calculated as,
Finally, the coefficient of the model can be found out,
Therefore, the value of coefficient is −11.4887, 7.1438, −1.0412 and 0.0467.
Now, for calculating the standard error follow these commands,
The standard error of the given data is 0.57.
Now for calculating 90% confidence levels for the coefficient, first calculate the inverse of [Z]T[Z] as,
Then the standard error of each coefficient,
The value of TINV(0.1,8−4)=TINV(0.1,4)=2.13185 is determined by the statistic t value calculator. Therefore, the 90% confidence levels for the coefficient is,
And,
Hence, the 90% confidence levels for the coefficient a0,a1,a2 and a3 is,
[−20.0253,−2.9521], [3.0378,11.2498],[−1.6302,−0.4522] and[0.0208, 0.0726] respectively.
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Chapter 17 Solutions
Numerical Methods for Engineers
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