"MagPlot[Transf, s, {w,wmin,wmax}, gopts]: Plots the magnitude part of Bode plot of transfer function Transf(s) in decibel(dB), from frequency w=wmin to w=wmax, both > 0 and in radians per second. Returns graphics.";
PhasePlot::usage =
"PhasePlot[Transf, s, {w,wmin,wmax}, gopts]: Plots the phase part of Bode plot of transfer function Transf(s) in degree, from frequency w=wmin to w=wmax; w is in radian per second.Returns graphics.";
LinearLogPlot::usage =
"LinearLogPlot[f, {x, xmin, xmax}] generates a plot of f as a function of x \
in log scale.";
NyquistPlot::usage =
"NyquistPlot[Transf, s, {w,wmin,wmax}, gopts]: Plots the Nyquist plot of the transfer function Transf(s). The plot is composed of three parts. The first part corresponds to s=jw with w=-wmin to w=-wmax. The second part corresponds to s=jw, w varying from w=+wmin to w=+wmax. Encirclement information of (-1+j0) is provided by the third part which corresponds to s with theta=-pi/2 to pi/2. wmin and wmax should be > 0 and radians per second. Returns graphics.";
Polar::usage =
"Polar[Transf, s, {w,wmin,wmax}, gopts]: Plots the polar plot of the transfer function Transf(s) with s=jw , w varying from w=wmin to w=wmax, both > 0 and in radians per second. Returns graphics.";
MagvsPhase::usage =
"MagvsPhase[Transf, s, {w,wmin,wmax}, gopts]: Plots the magnitude vs. phase plot of transfer function Transf(s) with s=jw. The frequency w varies from w=wmin to w=wmax both > 0 and in radians per second. Returns graphics.";
Modify::usage=
"Modify[x] returns a proper value for phase angle";