Log plot demo

Image obtained by using color PostScript driver (psc) and then converted to animated gif using ImageMagick convert tool.

 1 
 2 #pragma package "../"
 3 #include <chplplot.h>
 4 #include <math.h>
 5 #define PI M_PI
 6 
 7 void plot1(int type);
 8 
 9 
10 int
11 main(int argc, char *argv[])
12 {
13 
14     (void) plParseOpts(&argc, argv, PL_PARSE_FULL);
15 
16 
17     plinit();
18     plfont(2);
19 
20 
21     plot1(0);
22     plot1(1);
23 
24     plend();
25     exit(0);
26 }
27 
28 
29 void
30 plot1(int type)
31 {
32     int i;
33     static PLFLT freql[101], ampl[101], phase[101];
34     PLFLT f0, freq;
35 
36     pladv(0);
37 
38 
39     f0 = 1.0;
40     for (i = 0; i <= 100; i++) {
41 	freql[i] = -2.0 + i / 20.0;
42 	freq = pow(10.0, freql[i]);
43 	ampl[i] = 20.0 * log10(1.0 / sqrt(1.0 + pow((freq / f0), 2.)));
44 	phase[i] = -(180.0 / PI) * atan(freq / f0);
45     }
46 
47     plvpor(0.15, 0.85, 0.1, 0.9);
48     plwind(-2.0, 3.0, -80.0, 0.0);
49 
50 
51     plcol0(1);
52     switch (type) {
53     case 0:
54 	plbox("bclnst", 0.0, 0, "bnstv", 0.0, 0);
55 	break;
56     case 1:
57 	plbox("bcfghlnst", 0.0, 0, "bcghnstv", 0.0, 0);
58 	break;
59     }
60 
61 
62     plcol0(2);
63     plline(101, freql, ampl);
64     plcol0(1);
65     plptex(1.6, -30.0, 1.0, -20.0, 0.5, "-20 dB/decade");
66 
67 
68     plcol0(1);
69     plmtex("b", 3.2, 0.5, 0.5, "Frequency");
70     plmtex("t", 2.0, 0.5, 0.5, "Single Pole Low-Pass Filter");
71     plcol0(2);
72     plmtex("l", 5.0, 0.5, 0.5, "Amplitude (dB)");
73 
74 
75     if (type == 0) {
76 	plcol0(1);
77 	plwind(-2.0, 3.0, -100.0, 0.0);
78 	plbox("", 0.0, 0, "cmstv", 30.0, 3);
79 	plcol0(3);
80 	plline(101, freql, phase);
81 	plcol0(3);
82 	plmtex("r", 5.0, 0.5, 0.5, "Phase shift (degrees)");
83     }
84 }

Code description

1: $Id: x04c.c,v 1.17 2002/12/03 08:39:24 airwin Exp $ Log plot demo.
9: --------------------------------------------------------------------------*\ * main * * Illustration of logarithmic axes, and redefinition of window. \*--------------------------------------------------------------------------
13: Parse and process command line arguments
16: Initialize plplot
20: Make log plots using two different styles.
28: --------------------------------------------------------------------------*\ * plot1 * * Log-linear plot. \*--------------------------------------------------------------------------
38: Set up data for log plot
50: Try different axis and labelling styles.
61: Plot ampl vs freq
67: Put labels on
74: For the gridless case, put phase vs freq on same plot