# Bodegraph Argument Asymptotic Curve

The argument curve plotted by Bodegraph package gives the accurate plot. However, i am interested in drawing the approximate argument plot, same as the one you would get by drawing with hand on a graph paper, i.e., with fixed 45 degrees decrease per decade per pole.

The Asymptotic Argument curve only draws horizontal asymptotes (to my understanding) and differs from the approximate plot. The Asymtotic Amplitude plot gives the same approximate amplitude plot one would get by drawing with hand.

My question is that is there a way to plot the approximate argument curve using Bodegraph package?

A MWE showing the output of Bodegraph's Argument and Asymptotic Argument curve is shown. Furthermore, in the picture, the required approximate argument plot is also shown but is there a way to achieve that plot using some command of Bodegraph package.

\documentclass[border=5pt]{standalone}
\usepackage{bodegraph}
\begin{document}
\begin{tikzpicture} [>=latex',gnuplot def/.append style={prefix={}},
semilog lines/.style={gray},
semilog lines 2/.style={gray,dotted}]
\begin{scope}[xscale=8/4,yscale=4/90]
\OrdBode{45}
\semilog{0}{4}{-90}{0}
\BodeGraph[red,thick,samples=250]{0:4}{\POArgAsymp{1}{0.01}}
\BodeGraph[blue,thick,samples=250]{0:4}{\POArg{1}{0.01}}
\end{scope}
\end{tikzpicture}
\end{document}


• Sorry to revive an old question, but I am interested in this too, @rpapa, is there any way to incorporate something like this in bodegraph? The asymptotic phase plots in the Interactive Demos section on this page, for example? Aug 23 at 16:02

I added these more accurate asymptotic argument plots to the bodegraph package under the linear option. I do not know how to submit updated versions of packages to CTAN, but the updated package is on GitHub. Just make sure you use \BodeGraph[samples=300] (or more than 300 samples, depending on the slope of your argument plot) whenever there is a Asymp component in the plot.
Edit (10/25/21): I wrote a new package, called bodeplot, with a lot of added functionality. With that package, similar to the bode(zpk(...)) and bode(tf(...)) commands in MATLAB, you can now plot Bode (or Nyquist or Nichols) plots by directly entering the transfer function coefficients (\BodeTF) or lists of poles and zeros, delay, and gain (\BodeZPK). See https://github.com/rlkamalapurkar/bodeplot
• @KersouMan, the package has been updated to restore the original behavior for asymptotic plots. When loaded using the option linear, asymptotic plot commands generate the linear approximation asked for by the OP. Oct 17 at 5:32