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//
// math_lngamma_example.c
//
// Demonstrates accuracy of lngamma function
//
#include "liquid.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define OUTPUT_FILENAME "math_lngamma_example.m"
int main() {
unsigned int n = 256; // number of steps
float zmin = 1e-3f; // minimum value
float zmax = 6.00f; // maximum value
unsigned int d = n/32; // print every d values to screen
// log scale values
float xmin = logf(zmin);
float xmax = logf(zmax);
float dx = (xmax-xmin)/(n-1);
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
unsigned int i;
float z;
float g;
float x = xmin; // log(z)
for (i=0; i<n; i++) {
z = expf(x);
g = liquid_lngammaf(z);
fprintf(fid,"z(%4u) = %16.8e; g(%4u) = %16.8e;\n", i+1, z, i+1, g);
if ( (i%d)==0 )
printf("lngamma(%12.8f) = %12.8f\n",z,g);
x += dx;
}
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," semilogx(z,g,z,log(gamma(z)));\n");
fprintf(fid," xlabel('z');\n");
fprintf(fid," ylabel('lngamma(z)');\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," loglog(z,abs(log(gamma(z))-g));\n");
fprintf(fid," xlabel('z');\n");
fprintf(fid," ylabel('error');\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
return 0;
}
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