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from Numeric import *
from plplot import *
# main
#
# Illustration of logarithmic axes, and redefinition of window.
def main():
plfont(2)
plot1(0)
plot1(1)
# Restore defaults
plfont(1)
plcol0(1)
def plot1(type):
pladv(0)
f0 = 1.0
freql = -2.0 + arrayrange(101)/20.0
freq = pow(10.0, freql)
ampl = 20.0 * log10(1.0 / sqrt(1.0 + pow((freq / f0), 2.)))
phase = -(180.0 / pi) * arctan(freq / f0)
plvpor(0.15, 0.85, 0.1, 0.9)
plwind(-2., 3.0, -80.0, 0.0)
plcol0(1)
if type == 0:
plbox("bclnst", 0.0, 0, "bnstv", 0.0, 0)
elif type == 1:
plbox("bcfghlnst", 0.0, 0, "bcghnstv", 0.0, 0)
else:
print "error: type must be either 0 or 1"
plcol0(2)
plline(freql, ampl)
plcol0(1)
plptex(1.6, -30.0, 1.0, -20.0, 0.5, "-20 dB/decade")
# Put labels on
plcol0(1)
plmtex("b", 3.2, 0.5, 0.5, "Frequency")
plmtex("t", 2.0, 0.5, 0.5, "Single Pole Low-Pass Filter")
plcol0(2)
plmtex("l", 5.0, 0.5, 0.5, "Amplitude (dB)")
# For the gridless case, put phase vs freq on same plot
if type == 0:
plcol0(1)
plwind(-2.0, 3.0, -100.0, 0.0)
plbox("", 0.0, 0, "cmstv", 30.0, 3)
plcol0(3)
plline(freql, phase)
plcol0(3)
plmtex("r", 5.0, 0.5, 0.5, "Phase shift (degrees)")
main()
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