Find the least squares approximation

In summary, the problem is finding the least squares approximations for constants a and b in a set of data points that satisfy the relationship y = ax + b/x. This involves minimizing the sum of squares of the differences between the data points and the predicted values based on the relationship. To find the least squares approximations, the partial derivatives of the sum of squares function must be set to zero and solved for a and b.
  • #1
hsong9
80
1

Homework Statement


Suppose a set of N data points {(xk,yk)}Nk=1 appears to satisfy the relationship for some constants a and b. Find the least squares approximations for a and b.


Homework Equations





The Attempt at a Solution


I really have no idea about this problem.
 
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  • #2
You don't say what the relationship is, but let's say it's some function that we'll call [tex]y=f(x,a,b)[/tex]. The object of a least squares fit is to find [tex]a[/tex] and [tex]b[/tex] such that the sum of squares

[tex] S = \sum_{k-1}^N (y_k - f(x_k,a,b))^2[/tex]

is minimized.
 
  • #3
Thanks!
the relationship is y = ax + b/x.
Thus, S = Sigma ( y_k - (ax + b/x))^2, right?
and that's it?
 
  • #4
hsong9 said:
Thanks!
the relationship is y = ax + b/x.
Thus, S = Sigma ( y_k - (ax + b/x))^2, right?
and that's it?

S = Sigma ( y_k - (a x_k + b/x_k))^2

and you must minimize this as a function of a and b.
 
  • #5
Thanks!
So, to minimize S, set partial derivative for a and b equals to zero.
right?
Thanks again.
 

1. What is the purpose of finding the least squares approximation?

The purpose of finding the least squares approximation is to estimate the relationship between two variables by minimizing the sum of the squared differences between the actual data points and the predicted values. This technique is commonly used in regression analysis to identify the best-fit line or curve that represents the relationship between the variables.

2. How is the least squares approximation calculated?

The least squares approximation is calculated by finding the line or curve that minimizes the sum of the squared differences between the actual data points and the predicted values. This is done by finding the values for the slope and intercept that make the sum of squared differences as small as possible. This can be achieved using mathematical formulas or by using specialized software.

3. What are the assumptions made when using the least squares approximation?

The assumptions made when using the least squares approximation include: 1) linear relationship between the variables, 2) constant variance of the error terms, 3) independence of the error terms, and 4) normal distribution of the error terms. Violation of these assumptions can affect the accuracy of the approximation and may require alternative methods to be used.

4. How can I interpret the results of a least squares approximation?

The results of a least squares approximation can be interpreted by looking at the values of the slope and intercept. The slope represents the rate of change between the two variables, while the intercept represents the predicted value of the dependent variable when the independent variable is equal to zero. Additionally, the coefficient of determination (R-squared) can be used to measure the goodness of fit of the model, with higher values indicating a better fit.

5. What are the limitations of the least squares approximation?

The limitations of the least squares approximation include: 1) it assumes a linear relationship between the variables, which may not always be the case, 2) it requires the error terms to be normally distributed, 3) it may not be appropriate for non-linear relationships, and 4) it may be sensitive to outliers in the data. In these cases, alternative methods may need to be used to obtain a more accurate approximation.

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