ECIV 301 Programming & Graphics Numerical Methods for Engineers Lecture 25 Regression Analysis-Chapter 17
Curve Fitting Often we are faced with the problem… what value of y corresponds to x=0.935?
Curve Fitting Question 2 : Is it possible to find a simple and convenient formula that represents data approximately ? e.g. Best Fit ? Approximation
Experimental Measurements Strain Stress
Experimental Measurements Strain Stress
BEST FIT CRITERIA Strain y Stress Error at each Point Total Error
Best Fit => Minimize Error Not a Good Choice Not a Unique Best Fit
Best Fit => Minimize Error Try Absolute Not a Good Choice Not a Unique Best Fit
Best Fit => Minimize Error Best Strategy
Best Fit => Minimize Error Objective: What are the values of a o and a 1 that minimize ?
Least Square Approximation What x minimizes f(x)? Remember:
Least Square Approximation In our case Since x i and y i are known from given data
Least Square Approximation
2 Eqtns 2 Unknowns
Least Square Approximation
Example xyxyx2x a1= a0=
Example
Quantification of Error Average
Quantification of Error Average
Quantification of Error Average
Quantification of Error Standard Deviation Shows Spread Around mean Value
Quantification of Error
“Standard Deviation” for Linear Regression
Quantification of Error Better Representation Less Spread
Quantification of Error Coefficient of Determination Correlation Coefficient
Linearized Regression
Homework