1 //
2 // math_lngamma_example.c
3 //
4 // Demonstrates accuracy of lngamma function
5 //
6
7 #include "liquid.h"
8 #include <stdio.h>
9 #include <stdlib.h>
10 #include <math.h>
11
12 #define OUTPUT_FILENAME "math_lngamma_example.m"
13
main()14 int main() {
15 unsigned int n = 256; // number of steps
16 float zmin = 1e-3f; // minimum value
17 float zmax = 6.00f; // maximum value
18
19 unsigned int d = n/32; // print every d values to screen
20
21 // log scale values
22 float xmin = logf(zmin);
23 float xmax = logf(zmax);
24 float dx = (xmax-xmin)/(n-1);
25
26 FILE * fid = fopen(OUTPUT_FILENAME,"w");
27 fprintf(fid,"clear all;\n");
28 fprintf(fid,"close all;\n");
29 unsigned int i;
30 float z;
31 float g;
32 float x = xmin; // log(z)
33 for (i=0; i<n; i++) {
34 z = expf(x);
35 g = liquid_lngammaf(z);
36
37 fprintf(fid,"z(%4u) = %16.8e; g(%4u) = %16.8e;\n", i+1, z, i+1, g);
38 if ( (i%d)==0 )
39 printf("lngamma(%12.8f) = %12.8f\n",z,g);
40 x += dx;
41 }
42 fprintf(fid,"figure;\n");
43 fprintf(fid,"subplot(2,1,1);\n");
44 fprintf(fid," semilogx(z,g,z,log(gamma(z)));\n");
45 fprintf(fid," xlabel('z');\n");
46 fprintf(fid," ylabel('lngamma(z)');\n");
47 fprintf(fid,"subplot(2,1,2);\n");
48 fprintf(fid," loglog(z,abs(log(gamma(z))-g));\n");
49 fprintf(fid," xlabel('z');\n");
50 fprintf(fid," ylabel('error');\n");
51 fclose(fid);
52 printf("results written to %s.\n", OUTPUT_FILENAME);
53
54 return 0;
55 }
56