优秀例题——用最小二乘法画噪声数据的近似曲线

森之张卫东

1. <p>% Script file: lsqfit.m
   
2. % Purpose:
   
3. % To perform a leastsquares fit of an input data set
   
4. % to a straight line, and print out the resulting slope
   
5. % and intercept values. The input data for this fit
   
6. % comes from a userspecified input data file.
   
7. %
   
8. % Record of revisions:
   
9. % Date Programmer Description of change
   
10. % ==== ========== =====================
    
11. % 01/03/99 S. J. Chapman Original code
    
12. %
    
13. % Define variables:
    
14. % ii Loop index
    
15. % n_points Number in input [x y] points
    
16. % slope Slope of the line
    
17. % sum_x Sum of all input x values
    
18. % sum_x2 Sum of all input x values squared
    
19. % sum_xy Sum of all input x*y yalues
    
20. % sum_y Sum of all input y values
    
21. % temp Variable to read user input
    
22. % x Array of x values
    
23. % x_bar Average x value
    
24. % y Array of y values
    
25. % y_bar Average y value
    
26. % y_int yaxis intercept of the line
    
27. disp('This program performs a leastsquares fit of an ');
    
28. disp('input data set to a straight line.');
    
29. n_points = input('Enter the number of input [x y] points: ');
    
30. % Read the input data
    
31. for ii = 1:n_points
    
32. temp = input('Enter [x y] pair: ');
    
33. x(ii) = temp(1);
    
34. y(ii) = temp(2);
    
35. end
    
36. % Accumulate statistics
    
37. sum_x = 0;
    
38. sum_y = 0;
    
39. sum_x2 = 0;
    
40. sum_xy = 0;
    
41. for ii = 1:n_points
    
42.     sum_x = sum_x + x(ii);
    
43.     sum_y = sum_y + y(ii);
    
44.     sum_x2 = sum_x2 + x(ii)^2;
    
45.     sum_xy = sum_xy + x(ii) * y(ii);
    
46. end
    
47. % Now calculate the slope and intercept.
    
48. x_bar = sum_x / n_points;
    
49. y_bar = sum_y / n_points;
    
50. slope = (sum_xy - sum_x * y_bar) / ( sum_x2 - sum_x * x_bar);
    
51. y_int = y_bar - slope * x_bar;
    
52. % Tell user.
    
53. disp('Regression coefficients for the leastsquares line:');
    
54. fprintf(' Slope (m) = %8.3f\n', slope);
    
55. fprintf(' Intercept (b) = %8.3f\n', y_int);
    
56. fprintf(' No of points = %8d\n', n_points);
    
57. % Plot the data points as blue circles with no
    
58. % connecting lines.
    
59. plot(x,y,'bo');
    
60. hold on;
    
61. % Create the fitted line
    
62. xmin = min(x);
    
63. xmax = max(x);
    
64. ymin = slope * xmin + y_int;
    
65. ymax = slope * xmax + y_int;
    
66. % Plot a solid red line with no markers
    
67. plot([xmin xmax],[ymin ymax],'r','LineWidth',2);
    
68. hold off;
    
69. % Add a title and legend
    
70. title ('\bfLeastSquaresFit');
    
71. xlabel('\bf\itx');
    
72. ylabel('\bf\ity');
    
73. legend('Input data','Fitted line');
    
74. grid on
    
75. </p>

复制代码

森之张卫东

不错的例题，共同学习！！！

瞥神

非常好！！！！！！！！！！！！！！

614492427

66666666666666666666