void     read_data()
{
		 extern long    npt;
		 int            n;
         extern complex x[size];
         
		 for(n=0;n<size;++n)
		  {
		      x[n].real=0;
			  x[n].imag=0;
		  }
         
		 if ((in=fopen("list.dat","rt"))==NULL)
		 {
              printf("cannot open the file list.dat\n");
			  exit(1);
		 }
		 fscanf(in,"%ld",&npt);	
			 for(n=1;n<=npt;n++){
			    fscanf(in,"%lf %lf",&x[n].real,&x[n].imag);
				}
         fclose(in);
}