[Tex/LaTex] Trend line in pgf plot

errorspgfplotspgfplotstabletikz-pgf

I have been trying to fit a trend line using pgf plot for my data and unfortunately can't seem to hit the right spot with the code. I have looked in the manual for examples of linear regression and unfortunately it has been of no help. I already know the equation of the line from excel which calculates it to be $y=21208x+346.68$. Can anyone think of how I can fix this? To top it off now my code presented below is not correct!

    \documentclass{article}
    \usepackage{textcomp}
    \usepackage{pgfplots}
    \usepackage{pgfplotstable}
    \pgfplotsset{compat = newest}


    \begin{document}

    \begin{tikzpicture}
    \begin{axis}[
        title={BET Plot of Mesoporous Solid},
        xlabel={Relative pressure $P/P_0\times 10 ^{-3}$},
        ylabel={$\frac{P/P_0}{V(1-P/P_0)}$ [$m^{-3}$]},
        xmin=0, xmax=250,
        ymin=0, ymax=5000,
        xtick={0,50,100,150,200,250},
        ytick={0,1000,2000,3000,4000,5000},
        legend pos=north west,
        ymajorgrids=true,
        grid style=dashed,
    ]

    \addplot[
        color=black,
        mark=square,
        ]
        coordinates {
        (29.9025,905.43528)(63.7920,1716.5088)(97.6815,2471.0442)(122.6003,2977.7455)(145.5255,3470.4408)(174.4313,4060.0613)(194.3663,4448.5030)(208.3208,4708.7817) };

    \addplot[    
        \addplot table[y={create col/linear regression={y=Y}}]{
        (29.9025,905.43528)(63.7920,1716.5088)(97.6815,2471.0442)(122.6003,2977.7455)(145.5255,3470.4408)(174.4313,4060.0613)(194.3663,4448.5030)(208.3208,4708.7817) };

    \end{axis}
    \end{tikzpicture}
\end{document}

Best Answer

You use \addplot table, but then provide a coordinate stream instead of a table. Also, you say y=Y, but there's no column called Y in your data:

\documentclass{article}


    \usepackage{pgfplots}
    \usepackage{pgfplotstable}
    \pgfplotsset{compat = newest}


    \begin{document}

    \begin{tikzpicture}
    \begin{axis}[    
        title={BET Plot of Mesoporous Solid},
        xlabel={Relative pressure $P/P_0\times 10 ^{-3}$},
        ylabel={$\frac{P/P_0}{V(1-P/P_0)}$ [$m^{-3}$]},
        xmin=0, xmax=250,
        ymin=0, ymax=5000,
        xtick={0,50,100,150,200,250},
        ytick={0,1000,2000,3000,4000,5000},
        legend pos=north west,
        ymajorgrids=true,
        grid style=dashed,
    ]

    \addplot[
        color=black,
        mark=square,
        ]
        coordinates {
        (29.9025,905.43528)(63.7920,1716.5088)(97.6815,2471.0442)(122.6003,2977.7455)(145.5255,3470.4408)(174.4313,4060.0613)(194.3663,4448.5030)(208.3208,4708.7817) };

        \addplot [thick, red] table[y={create col/linear regression}]{
        29.9025 905.43528
        63.7920 1716.5088
        97.6815 2471.0442
        122.6003 2977.7455
        145.5255 3470.4408
        174.4313 4060.0613
        194.3663 4448.5030
        208.3208 4708.7817
        };



    \end{axis}
    \end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Trend line with pgfplots and dateplots

In general, you can always customize your tick labels manually, without resorting to date coordinates in or symbolic coords. For the records here, I will show how (see my second example in this answer) even though I have something which might fit better (my first example).

But since you asked for some "more efficient one-liner", I found one for you by combining the available styles for xticklabels from table with date coordinates in:

\documentclass{minimal}
\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}
\begin{filecontents}{data.dat}
date            value1
2010-01-01      2
2010-01-02      10
2010-01-03      8
2010-01-04      15
\end{filecontents}
\usepackage{pgfplotstable}

% formats row \ticknum of the input table using '#3'
% #1: table name
% #2: column name
% #3: formatting instruction like \day.\month.\year
\newcommand\datelabelsfromtable[3]{%
    \begingroup
    \countdef\result=\count200 %
    \pgfplotstablegetelem{\ticknum}{#2}\of{#1}%
    \pgfcalendardatetojulian{\pgfplotsretval}{\result}%
    \pgfcalendarjuliantodate{\result}\year\month\day
    %
    #3%
    \endgroup
}

\begin{document}
\begin{tikzpicture}

\begin{axis}[
    x tick label style={yshift=-3pt,xshift=-4pt,rotate=-30,anchor=west},
    xticklabel={\datelabelsfromtable{data.dat}{date}{\day.\month.\year}},
    xtick=data,
]
\addplot table [x expr=\coordindex,y=value1] {data.dat};
\addplot table [x expr=\coordindex, y={create col/linear regression={y=value1}}] {data.dat};
\end{axis}

\end{tikzpicture}
\end{document}

enter image description here

The answer above is a little bit complicated because the public \pgfcalendar* utility functions require a TeX counter on input and I did not want to waste one with \newcounter. The \countdef simply reuses an existing counter, but the effect is limited by the fact that the assignment is local to a group. The rest of that utility function is rather straight-forward: extract the desired entry from the input table, parse it as date, then convert the parsed representation to the desired output date format. This is not quite as powerful as the dateplot library because it does not compute tick labels automatically and because it does not support hours and minutes, but for the moment, it appears to be the most "one-line" solution at hand.

Note that \addplot table uses x expr=\coordindex, i.e. the row number as x coordinate.

Just for the records, I would like to stress that assigning tick labels manually is always possible, just as for any other plotting tool. Since xticklabels from table does not use the expected output date format, I would use the following for the minimal example:

\documentclass{minimal}
\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}
\begin{filecontents}{data.dat}
date            value1
2010-01-01      2
2010-01-02      10
2010-01-03      8
2010-01-04      15
\end{filecontents}
\usepackage{pgfplotstable}
\begin{document}
\begin{tikzpicture}

\begin{axis}[
    x tick label style={yshift=-3pt,xshift=-4pt,rotate=-30,anchor=west},
    xticklabels={01.01.2010, 02.01.2010, 03.01.2010, 04.01.2010},
    xtick=data,
]
\addplot table [x expr=\coordindex,y=value1] {data.dat};
\addplot table [x expr=\coordindex, y={create col/linear regression={y=value1}}] {data.dat};
\end{axis}

\end{tikzpicture}
\end{document}

The outcome is precisely the same as above.

[Tex/LaTex] plotting two time series with bounds

This happens because PGFPlots only uses one "stack" per axis: You're stacking the second confidence interval on top of the first. The easiest way to fix this is probably to use the approach described in "Is there an easy way of using line thickness as error indicator in a plot?": After plotting the first confidence interval, stack the upper bound on top again, using stack dir=minus. That way, the stack will be reset to zero, and you can draw the second confidence interval in the same fashion as the first:

\documentclass{standalone}
\usepackage{pgfplots, tikz}

\usepackage{pgfplotstable}

\pgfplotstableread{
temps   y_h y_h__inf    y_h__sup    y_f y_f__inf    y_f__sup    

1   0.237340    0.135170    0.339511    0.237653    0.135482    0.339823    
2   0.561320    0.422007    0.700633    0.165871    0.026558    0.305184    
3   0.694760    0.534205    0.855314    0.074856    -0.085698   0.235411    
4   0.728306    0.560179    0.896432    0.003361    -0.164765   0.171487    
5   0.711710    0.544944    0.878477    -0.044582   -0.211349   0.122184    
6   0.671241    0.511191    0.831291    -0.073347   -0.233397   0.086703    
7   0.621177    0.471219    0.771135    -0.088418   -0.238376   0.061540    
8   0.569354    0.431826    0.706882    -0.094382   -0.231910   0.043146    
9   0.519973    0.396571    0.643376    -0.094619   -0.218022   0.028783    
10  0.475121    0.366990    0.583251    -0.091467   -0.199598   0.016664    
}{\table}

\begin{document}
\begin{tikzpicture}

    \begin{axis}
    % y_h confidence interval
    \addplot [stack plots=y, fill=none, draw=none, forget plot]   table [x=temps, y=y_h__inf]   {\table} \closedcycle;
    \addplot [stack plots=y, fill=gray!50, opacity=0.4, draw opacity=0, area legend]   table [x=temps, y expr=\thisrow{y_h__sup}-\thisrow{y_h__inf}]   {\table} \closedcycle;
    % subtract the upper bound so our stack is back at zero
    \addplot [stack plots=y, stack dir=minus, forget plot, draw=none] table [x=temps, y=y_h__sup] {\table};

    % y_f confidence interval
    \addplot [stack plots=y, fill=none, draw=none, forget plot]   table [x=temps, y=y_f__inf]   {\table} \closedcycle;
    \addplot [stack plots=y, fill=gray!50, opacity=0.4, draw opacity=0, area legend]   table [x=temps, y expr=\thisrow{y_f__sup}-\thisrow{y_f__inf}]   {\table} \closedcycle;

    % the line plots (y_h and y_f)    
    \addplot [stack plots=false, very thick,smooth,blue]  table [x=temps, y=y_h]   {\table};
    \addplot [stack plots=false, very thick,smooth,blue]  table [x=temps, y=y_f]   {\table};
    \end{axis}

\end{tikzpicture}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Trend line with pgfplots and dateplots

[Tex/LaTex] plotting two time series with bounds

Related Question