To determine the straightness error it is necessary to fit a straight to the set points measured. The linear model to be fit is given by Eq. (4), where εi is the residual value and a1,a2 are the parameters to be calculated.
สูตรที่ (4)
The residual value is a random variable, independently and identically distributed, that is with normal distribution of mean zero and variance constant.
As previously stated, the LSM minimize the sum of the square of the residual and, therefore, to fit the points to a straight the following sum is minimized:
สูตรที่ (5)
To minimize Eq. (5), the partial derivatives of S with respect to a1 and a2 have to be null. By this way, can be obtained the following expressions, Eq. (6), called normal expressions.
สูตรที่ (6)
Solving Eq. (6), the parameters of LSM can be given by Eq. (7), where x and y are the arithmetic averages of xi and yi , respectively.
สูตรที่ (7)
Equation (7) are always the only solution for Eq. (5) if not all xi are the same.
This way, the straight, which fits better to the points, can be chosen, Eq. (8).
สูตรที่ (8)
To determine the straightness error it is necessary to fit a straight to the set points measured. The linear model to be fit is given by Eq. (4), where εi is the residual value and a1,a2 are the parameters to be calculated. สูตรที่ (4) The residual value is a random variable, independently and identically distributed, that is with normal distribution of mean zero and variance constant. As previously stated, the LSM minimize the sum of the square of the residual and, therefore, to fit the points to a straight the following sum is minimized: สูตรที่ (5) To minimize Eq. (5), the partial derivatives of S with respect to a1 and a2 have to be null. By this way, can be obtained the following expressions, Eq. (6), called normal expressions. สูตรที่ (6) Solving Eq. (6), the parameters of LSM can be given by Eq. (7), where x and y are the arithmetic averages of xi and yi , respectively. สูตรที่ (7) Equation (7) are always the only solution for Eq. (5) if not all xi are the same. This way, the straight, which fits better to the points, can be chosen, Eq. (8). สูตรที่ (8)
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