# how to draw plots without data in tikz?

I want to draw this plot. I know how to do it with data. But here I don't have any data. And I want to draw this. How would I do it?

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What you need is an expression for the function drawn by these dots. As such, maybe this question would be a better fit for math.stackexchange.com or stats.stackexchange.com . – T. Verron Feb 12 '13 at 7:11
What you mean by draw plot without data? Do you want the axes only? Do you want to extract the data somehow from the image you have? – Psirus Feb 12 '13 at 7:12
I don't have equation or the data. Is there any way to extract the data from this? Or how to find the equation and plot it? – tikzlearner Feb 12 '13 at 7:31
@user1280282: The function is given in the metadata for the Wikipedia image you posted. – Jake Feb 12 '13 at 7:33

As others have said, if you don't have the data values, you need to generate them using a function. The easiest way is to use PGFPlots and simply plot a function f(x) where x is sampled at regular intervals within some range. For example, to plot f(x)=x^3, you could use the following code:

\documentclass{article}
\usepackage{pgfplots}
\begin{document}

\begin{tikzpicture}
\begin{axis}
\addplot [only marks, fill=cyan, mark size=1.5] {x^3};
\end{axis}
\end{tikzpicture}

\end{document}


For more complicated functions, and especially when your x samples aren't regularly spaced, you can either calculate the data outside of TeX and simply include it in your document, or you could use PGFPlotstable to generate a data table inside the document.

Here's an example where I created a table with three columns: x, an intermediate step, and y, based on the code found in the metadata included with the Wikipedia image you used:

\documentclass{article}
\usepackage{pgfplots, pgfplotstable}
\begin{document}

\pgfplotstablenew[
create on use/x/.style={
create col/expr={rnd}
},
create on use/intermediate/.style={
create col/expr={ln(\thisrow{x}/(1-\thisrow{x}))}
},
create on use/y/.style={
create col/expr={
\thisrow{intermediate}/(abs(\thisrow{intermediate}))*abs(\thisrow{intermediate})^1.4
}
},
columns={x,intermediate, y}]
{75}
\datatable

\begin{tikzpicture}
\begin{axis}
\addplot [only marks, fill=cyan, mark size=1.5] table [x=x, y=y] {\datatable};
\end{axis}
\end{tikzpicture}

\end{document}

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Don't try it for "real" scientific papers, of course. :-) – T. Verron Feb 12 '13 at 7:40
@T.Verron: Not without adding some noise, of course, otherwise people will get suspicious! – Jake Feb 12 '13 at 7:41