#include <stdio.h>
#include <math.h>
void mk_triangle_data(char *a, double x1, double x2, int n);
void mk_graph(char *f, char *xlb, double x1, double x2,
	      char *ylb, double y1, double y2);

/*==========================================================*/
/*   main function                                          */
/*==========================================================*/
int main(void){

  double pi = 4*atan(1);
  
  mk_triangle_data("out.txt", -2*pi, 2*pi, 1000);
  mk_graph("out.txt", "x", -2*pi, 2*pi, "y", -3, 3);
  
  return 0;
}

/*==========================================================*/
/*   make a data file                                       */
/*==========================================================*/
void mk_triangle_data(char *a, double x1, double x2, int n){
  double x, dx;
  double y1, y2, y3;
  int i;
  FILE *out;
  
  dx = (x2-x1)/n;
  
  out = fopen(a, "w");
  
  for(i=0; i<=n; i++){
    x = x1+dx*i;
    y1 = sin(x);
    y2 = cos(x);
    y3 = tan(x);
    
    fprintf(out, "%e\t%e\t%e\t%e\n", x, y1, y2, y3);
  }
  
  fclose(out);
}

/*==========================================================*/
/*   make a graph                                           */
/*==========================================================*/
void mk_graph(char *f, char *xlb, double x1, double x2,
	      char *ylb, double y1, double y2)
{
  
  FILE *gp;
  
  gp = popen("gnuplot -persist","w");
  
  fprintf(gp, "reset\n");

  /* -------  set x grid ---------*/

  fprintf(gp, "set grid\n");
  
  /* -------  set x axis ---------*/
  
  fprintf(gp, "set xtics 1\n");
  fprintf(gp, "set mxtics 10\n");
  fprintf(gp, "set xlabel \"%s\"\n", xlb);
  fprintf(gp, "set nologscale x\n");
  fprintf(gp, "set xrange[%e:%e]\n", x1, x2);
  
  /* -------  set y axis ---------*/
  
  fprintf(gp, "set ytics 1\n");
  fprintf(gp, "set mytics 10\n");
  fprintf(gp, "set ylabel \"%s\"\n", ylb);
  fprintf(gp, "set nologscale y\n");
  fprintf(gp, "set yrange[%e:%e]\n", y1, y2);
  
        /* -------  plat graphs ---------*/

  fprintf(gp, "set terminal x11\n");
  
  fprintf(gp, "plot \"%s\" using 1:2 with line,\
                    \"%s\" using 1:3 with line,\
                    \"%s\" using 1:4 with line\n", f, f, f);
  
  fprintf(gp, "set terminal emf\n");
  fprintf(gp, "set output \"tri.emf\"\n");

  fprintf(gp, "replot\n");
  
  pclose(gp);
}