/******************************************************************************************************
Treibergs                                                                                        4-13-6

Gnuplot Driver 1

Program to write data files and execution files that run the plotting software  gnuplot  from a C 
program. Thanks to Prof. G. Gustafson for showing me how to do this.


drivegnuplo.c
******************************************************************************************************/

# include <stdio.h>
# include <stdlib.h>
# include <math.h>


double                   /* Function prototype.                             */
perfun ( double x, double p );

int
main( void )
{

    double a, b, c, d, p, x;
    int i;
    FILE *fp;                            /* Declaration of file variable */


   
   printf ( "Periodic Function Via Recursive Function Calls\n" );  
   printf ( " Enter period : " );
   scanf ( "%lf", &p );

   printf ( " Enter two endpoint values : " );
   scanf ( "%lf %lf", &a, &b );

   if ( b < a)
   {                     /*  Swap  a  and  b  if  b < a.                     */
             c = a;
             a = b;
             b = c;
    }
    d = ( b - a ) / 300.0;

    fp = fopen ( "commands.gplot", "w" );    /* Open commands file */
                                         /* fopen returns a pointer to the file. */
                                         /* "w" for writing files, "r" for reading. */

    fprintf ( fp, "plot [ %f : %f ] \'fn.dat\' w lines, 0 \n", a - d, b + d  );     
    fprintf ( fp, "pause mouse \n" );    
    fclose ( fp );                        /* closing returns file to system. */
                                          /* Newly written data may be lost without closing the file */


              
    printf ( "\nFunction values from %f to %f  are being printed to file \"fn.dat\"\n", a, b );
 
    fp = fopen ( "fn.dat", "w" );    /* Open data file. */

    for ( i = 0;  i <= 300 ;  i++ )
    {
             x = a  +  i * d;
             fprintf ( fp, "%25.15f  %25.15f\n", x, perfun ( x, p ) );
    }  
                  

    fclose( fp );

    system("gnuplot commands.gplot");




    return EXIT_SUCCESS;
}


/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

double
perfun ( double x, double p )
{                    
                       /* perfun grows linearly from 0 to p/4, then droops.    */
      double result;
      
      if ( x < 0.0 )
              result = perfun ( x + p, p );
      else if ( x >= p )
              result = perfun ( x - p, p );
      else
      {
             if( x <= 0.25*p)
                   result = 16.0 * x / p;
             else
                   result = 1.0 / ( 0.25  +  x / p )  -  1.0;
       }
       
      return result;
 }