1 //
2 // polyfit_example.c
3 //
4 // Test polynomial fit to sample data.
5 //
6
7 #include <stdio.h>
8
9 #include "liquid.h"
10
11 #define OUTPUT_FILENAME "polyfit_example.m"
12
main()13 int main() {
14
15 unsigned int n=15; // number of samples
16 unsigned int order=2; // polynomial order
17
18 FILE * fid = fopen(OUTPUT_FILENAME, "w");
19 fprintf(fid,"%% %s : auto-generated file\n\n", OUTPUT_FILENAME);
20 fprintf(fid,"clear all;\nclose all;\n\n");
21
22 // initialize data vectors
23 float x[n];
24 float y[n];
25 unsigned int i;
26 for (i=0; i<n; i++) {
27 float v = (float)(i) - (float)(n)/2 + 0.5f;
28 x[i] = v;
29 y[i] = v*v + randnf();
30
31 printf("x : %12.8f, y : %12.8f\n", x[i], y[i]);
32 fprintf(fid,"x(%3u) = %12.4e; y(%3u) = %12.4e;\n", i+1, x[i], i+1, y[i]);
33 }
34
35 // compute coefficients
36 unsigned int k=order+1;
37 float p[k];
38 polyf_fit(x,y,n,p,k);
39
40 for (i=0; i<k; i++) {
41 printf("p[%3u] = %12.4e\n", i, p[i]);
42 // print polynomial coefficients vector in reverse order
43 fprintf(fid,"p(%3u) = %12.4e;\n", i+1, p[k-i-1]);
44 }
45
46 // evaluate polynomial
47 float xmin = -7.5f;
48 float xmax = 7.5f;
49 unsigned int num_steps = 64;
50 float dx = (xmax-xmin)/(num_steps-1);
51 float xtest = xmin;
52 float ytest;
53 for (i=0; i<num_steps; i++) {
54 ytest = polyf_val(p,k,xtest);
55 fprintf(fid,"xtest(%3u) = %12.4e; ytest(%3u) = %12.4e;\n", i+1, xtest, i+1, ytest);
56 xtest += dx;
57 }
58
59 // plot results
60 fprintf(fid,"plot(x,y,'x',xtest,ytest,'-');\n");
61 fprintf(fid,"xlabel('x');\n");
62 fprintf(fid,"ylabel('y, p^{(%u)}(x)');\n", order);
63 fprintf(fid,"legend('data','poly-fit',0);\n");
64 fprintf(fid,"grid on;\n");
65
66 fclose(fid);
67 printf("results written to %s\n", OUTPUT_FILENAME);
68
69 printf("done.\n");
70 return 0;
71 }
72
73