1 /*
2 * Library: lmfit (Levenberg-Marquardt least squares fitting)
3 *
4 * File: demo/curve1.c
5 *
6 * Contents: Example for fitting data with error bars:
7 * fit a data set (x,y+-dy) by a curve f(x;p).
8 *
9 * Author: Joachim Wuttke <j.wuttke@fz-juelich.de> 2004-2013
10 *
11 * Licence: see ../COPYING (FreeBSD)
12 *
13 * Homepage: apps.jcns.fz-juelich.de/lmfit
14 */
15
16 #include "lmcurve_tyd.h"
17 #include <stdio.h>
18
19 /* model function: a parabola */
20
f(double t,const double * p)21 double f( double t, const double *p )
22 {
23 return p[0] + p[1]*t + p[2]*t*t;
24 }
25
main()26 int main()
27 {
28 int n = 3; /* number of parameters in model function f */
29 double par[3] = { 100, 0, -10 }; /* really bad starting value */
30
31 /* data points: a slightly distorted standard parabola */
32 int m = 9;
33 int i;
34 double t[9] = { -4., -3., -2., -1., 0., 1., 2., 3., 4. };
35 double y[9] = { 16.6, 9.9, 4.4, 1.1, 0., 1.1, 4.2, 9.3, 16.4 };
36 double dy[9] = { 4, 3, 2, 1, 2, 3, 4, 5, 6 };
37
38 lm_control_struct control = lm_control_double;
39 lm_status_struct status;
40 control.verbosity = 1;
41
42 printf( "Fitting ...\n" );
43 /* now the call to lmfit */
44 lmcurve_tyd( n, par, m, t, y, dy, f, &control, &status );
45
46 printf( "Results:\n" );
47 printf( "status after %d function evaluations:\n %s\n",
48 status.nfev, lm_infmsg[status.outcome] );
49
50 printf("obtained parameters:\n");
51 for ( i = 0; i < n; ++i)
52 printf(" par[%i] = %12g\n", i, par[i]);
53 printf("obtained norm:\n %12g\n", status.fnorm );
54
55 printf("fitting data as follows:\n");
56 for ( i = 0; i < m; ++i)
57 printf(
58 " t[%1d]=%2g y=%5.1f+-%4.1f fit=%8.5f residue=%8.4f weighed=%8.4f\n",
59 i, t[i], y[i], dy[i], f(t[i],par), y[i] - f(t[i],par),
60 (y[i] - f(t[i],par))/dy[i] );
61
62 return 0;
63 }
64