/* Illustration of logarithmic axes, and redefinition of window */

#include <math.h>

main()
{
      int i;
      float freql[101],ampl[101],phase[101];
      float f0, freq;

      plstar(1,1);
      pladv(0);
      plfont(2);

      f0 = 1000.0;
      for (i=0; i<=100; i++) {
        freql[i]=1.0+i/20.0;
        freq= pow(10.0,freql[i]);
        ampl[i]=20.0*log10(1.0/sqrt(1.0+pow((freq/f0),2.)));
        phase[i]=-(180.0/3.141592654)*atan(freq/f0);
      }

      plvpor(0.15,0.85,0.1,0.9);
      plwind(1.0,6.0,-80.0,0.0);
      plbox("bclnst",0.0,0,"bnstv",0.0,0);
      plline(101,freql,ampl);
      plptex(5.0,-30.0,1.0,-20.0,0.5,"-20 dB/decade");
      plwind(1.0,6.0,-100.0,0.0);
      plbox(" ",0.0,0,"cmstv",30.0,3);
      plline(101,freql,phase);

      plmtex("b",3.2,0.5,0.5,"Frequency");
      plmtex("t",2.0,0.5,0.5,"Single Pole Low-Pass Filter");
      plmtex("l",5.0,0.5,0.5,"Amplitude (dB)");
      plmtex("r",5.0,0.5,0.5,"Phase shift (degrees)");

      plend();
}