# Shift addplot on x axis to match end of another plot

Hello and happy new year,

I am trying to create a continuous plot made of two different functions. Altough I am able to calculate and plot both of them correctly, I am not able to make the second function start on the end of the first one:

Both functions are calculated starting at a time of 0, but the red line should start at the end of the blue line, so it needs to be shifted to 0.2ns. I have tried using shift={(0.2,0)} on the second plot, but the data appears far away.

PS: I know that the red line appears on 0 because its domain is defined from 0 to 3.

My tex file is as follows:

\documentclass[class=IEEEtran]{standalone}
\usepackage{pgfplots}
\begin{document}

%- Declare parameters
\usetikzlibrary{math} % For computations. Variables must be declared in a tikzmath environment but can be used outside (almost anywhere)
\tikzmath{
\Qfactor = 500; % Quality factor
\f0 =230; % Freq in GHz
\TimeConst = \Qfactor/(pi*\f0);
\finalCharge = exp(-2*0.2/\TimeConst)-1; % Initial value for ringing tail
}
\begin{tikzpicture}
\begin{axis}[
axis lines = left,
xmin=0, xmax=3,
ymin=-30, ymax=5,
ytick = {-30,-25,-20,-15,-10,-5,0,5},
ylabel = { Normalized power (dB)},
xlabel = {Time (ns)},
width=3.15in,
height=2.15in,
]
\addplot+[no marks, domain=0:0.2,samples = 10] plot (\x, {10*log10(abs(exp(-2*\x/\TimeConst)-1))});
% PLOT TO SHIFT:
\addplot+[no marks, domain=0:3,samples = 50] plot (\x, {10*log10(abs(\finalCharge*exp(-2*\x/\TimeConst)))});
\end{axis}
\end{tikzpicture}
\end{document}


You can achieve this by simple math:

\documentclass[class=IEEEtran]{standalone}
\usepackage{pgfplots}
\begin{document}

%- Declare parameters
\usetikzlibrary{math} % For computations. Variables must be declared in a tikzmath environment but can be used outside (almost anywhere)
\tikzmath{
\Qfactor = 500; % Quality factor
\f0 =230; % Freq in GHz
\TimeConst = \Qfactor/(pi*\f0);
\finalCharge = exp(-2*0.2/\TimeConst)-1; % Initial value for ringing tail
}
\begin{tikzpicture}
\begin{axis}[
axis lines = left,
xmin=0, xmax=3,
ymin=-30, ymax=5,
ytick = {-30,-25,-20,-15,-10,-5,0,5},
ylabel = { Normalized power (dB)},
xlabel = {Time (ns)},
width=3.15in,
height=2.15in,
]
\addplot+[no marks, domain=0:0.2,samples = 10] plot (\x, {10*log10(abs(exp(-2*\x/\TimeConst)-1))});
% PLOT TO SHIFT:
\addplot+[no marks, domain=0.2:3,samples = 50] plot
(\x, {
10 * log10 (abs( \finalCharge * exp(-2 * (x - 0.2) / \TimeConst) ))
}
);
\end{axis}
\end{tikzpicture}
\end{document}


I don't really now know what the difference between \x and a regular x is, but you can also use (\x - 0.2) instead of (x - 0.2) if you want.

That's my output:

• I didn't even think about doing this... shame on me. Thanks for the remark about \x!
– Jes
Jan 5 '21 at 11:37