Line of best fit with equations

Question

New to LaTeX, and was hoping someone would be kind enough to give me a hand with trying to draw lines of best fit to these data points. I have included the example I am working on.

\documentclass[]{article}
\usepackage{filecontents,pgfplots}
\usepackage{pgfplotstable}
% recommended:
\usepackage{booktabs}
\usepackage{array}
\usepackage{colortbl}
%\usepgfplotslibrary{clickable}
\pgfdeclareplotmark{halfcircle}{%
\begin{pgfscope}
\pgfsetfillcolor{white}%
\pgfpathcircle{\pgfpoint{0pt}{0pt}}
{\pgfplotmarksize}
\pgfusepathqfillstroke
\end{pgfscope}%
\pgfpathmoveto
{\pgfpoint{\pgfplotmarksize}{0pt}}
\pgfpatharc{0}{180}{\pgfplotmarksize}
\pgfpathclose
\pgfusepathqfill
}

\begin{filecontents}{conductivity.dat}
L(cm)   50mA    100mA  200mA 400mA 800mA 1000mA
0.0000  0.0000 0.0000 0.000 0.000 0.000 0.000
2.0000  0.0342 0.0635 0.128 0.260 0.520 0.650
3.0000  0.0555 0.1043 0.212 0.423 0.840 1.030
4.0000  0.1104 0.2064 0.396 0.809 1.300 1.700
6.0000  0.1350 0.2426 0.502 1.034 2.010 2.471
7.0000  0.1669 0.3326 0.673 1.339 2.610 3.140

\end{filecontents}

\begin{document}
\pgfplotstableread{conductivity.dat}{\conductivity}
\centering
\begin{tikzpicture}[scale=1]
\begin{axis}[xmin = 0, ymin = 0,
            xlabel=Bed depth (cm),
            ylabel = Voltage, 
            width=1.2\textwidth,
            height=0.8\textwidth, legend pos={north west},
            xticklabel style={/pgf/number format/1000 sep=}]
\addplot+[only marks][black, mark = otimes] table [x={L(cm)}, y={50mA}] {\conductivity};\addlegendentry{50mA}
\addplot+[only marks] [mark = star, black] table [x={L(cm)}, y={100mA}] {\conductivity};\addlegendentry{100mA}
\addplot+[only marks] [mark = o, black ] table [x={L(cm)}, y={200mA}] {\conductivity};\addlegendentry{200mA}
\addplot+[only marks] [mark = +, black] table [x={L(cm)}, y={400mA}] {\conductivity};\addlegendentry{400mA}
\addplot+[only marks] [mark = oplus, black] table [x={L(cm)}, y={800mA}] {\conductivity};\addlegendentry{800mA}
\addplot+[only marks] [mark=halfcircle, black] table [x={L(cm)}, y={1000mA}] {\conductivity};\addlegendentry{1000mA}
\end{axis}
\end{tikzpicture}

\end{document}

Answer 1

Does this fit your needs? I added the values of the regression lines for each voltage to the \conductivity table with the command \pgfplotstablecreatecol. Then you can use easily use those values in plots or use pgfplotstable to give you a table containing the values.

\documentclass[]{article}
\usepackage{filecontents,pgfplots}
\usepackage{pgfplotstable}
% recommended:
\usepackage{booktabs}
\usepackage{array}
\usepackage{colortbl}
%\usepgfplotslibrary{clickable}
\pgfdeclareplotmark{halfcircle}{%
\begin{pgfscope}
\pgfsetfillcolor{white}%
\pgfpathcircle{\pgfpoint{0pt}{0pt}}
{\pgfplotmarksize}
\pgfusepathqfillstroke
\end{pgfscope}%
\pgfpathmoveto
{\pgfpoint{\pgfplotmarksize}{0pt}}
\pgfpatharc{0}{180}{\pgfplotmarksize}
\pgfpathclose
\pgfusepathqfill
}

\begin{filecontents}{conductivity.dat}
L(cm)   50mA    100mA  200mA 400mA 800mA 1000mA
0.0000  0.0000 0.0000 0.000 0.000 0.000 0.000
2.0000  0.0342 0.0635 0.128 0.260 0.520 0.650
3.0000  0.0555 0.1043 0.212 0.423 0.840 1.030
4.0000  0.1104 0.2064 0.396 0.809 1.300 1.700
6.0000  0.1350 0.2426 0.502 1.034 2.010 2.471
7.0000  0.1669 0.3326 0.673 1.339 2.610 3.140

\end{filecontents}

\begin{document}
\pgfplotstableread{conductivity.dat}{\conductivity}
% create the `regression' columns:
\pgfplotstablecreatecol[linear regression={y=50mA}]{regression 50mA}{\conductivity}
\pgfplotstablecreatecol[linear regression={y=100mA}]{regression 100mA}{\conductivity}
\pgfplotstablecreatecol[linear regression={y=200mA}]{regression 200mA}{\conductivity}
\pgfplotstablecreatecol[linear regression={y=400mA}]{regression 400mA}{\conductivity}
\pgfplotstablecreatecol[linear regression={y=800mA}]{regression 800mA}{\conductivity}
\pgfplotstablecreatecol[linear regression={y=1000mA}]{regression 1000mA}{\conductivity}

\centering
\begin{tikzpicture}[scale=1]
\begin{axis}[xmin = 0, ymin = 0,
            xlabel=Bed depth (cm),
            ylabel = Voltage, 
            width=1.2\textwidth,
            height=0.8\textwidth, legend pos={north west},
            xticklabel style={/pgf/number format/1000 sep=}]
% regression
\addplot[black, no markers] table [x={L(cm)}, y={regression 50mA}] {\conductivity};\addlegendentry{50mA}
\addplot[orange, no markers] table [x={L(cm)}, y={regression 100mA}] {\conductivity};\addlegendentry{100mA}
\addplot[magenta, no markers] table [x={L(cm)}, y={regression 200mA}] {\conductivity};\addlegendentry{200mA}
\addplot[green, no markers] table [x={L(cm)}, y={regression 400mA}] {\conductivity};\addlegendentry{400mA}
\addplot[blue, no markers] table [x={L(cm)}, y={regression 800mA}] {\conductivity};\addlegendentry{800mA}
\addplot[red, no markers] table [x={L(cm)}, y={regression 1000mA}] {\conductivity};\addlegendentry{1000mA}
% data 
\addplot+[only marks][black, mark = otimes] table [x={L(cm)}, y={50mA}] {\conductivity};\addlegendentry{50mA}
\addplot+[only marks] [mark = star, black] table [x={L(cm)}, y={100mA}] {\conductivity};\addlegendentry{100mA}
\addplot+[only marks] [mark = o, black ] table [x={L(cm)}, y={200mA}] {\conductivity};\addlegendentry{200mA}
\addplot+[only marks] [mark = +, black] table [x={L(cm)}, y={400mA}] {\conductivity};\addlegendentry{400mA}
\addplot+[only marks] [mark = oplus, black] table [x={L(cm)}, y={800mA}] {\conductivity};\addlegendentry{800mA}
\addplot+[only marks] [mark=halfcircle, black] table [x={L(cm)}, y={1000mA}] {\conductivity};\addlegendentry{1000mA}
\end{axis}
\end{tikzpicture}

\pgfplotstabletypeset[columns={50mA, 100mA, 200mA, 400mA, 800mA, 1000mA}]\conductivity\\

\pgfplotstabletypeset[columns={regression 50mA, regression 100mA, regression 200mA, regression 400mA, regression 800mA}]\conductivity
\end{document}