# how to print variable value of \draw function

I use this function:

\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15}

\begin{document}
\newcommand{\xmax}{14}
\newcommand{\fmin}{(pi/3)}
\newcommand{\fmax}{(2*pi)}
\begin{tikzpicture}
[domain=\xmax:0, samples=500]

% The following line uses linear frequency increase
%\draw[ultra thick, red] plot (\x, {sin(deg((\fmin+\x*((\fmax-\fmin))/\xmax)*\x))} );
% The following line uses exponential frequency increase
\draw[ultra thick, red] plot (\x, {sin(deg(exp(ln(\fmin)+\x/\xmax*(ln(\fmax)-ln(\fmin)))*\x))} );
\end{tikzpicture}
\end{document}


I need to evaluate the \x parameter. How can I print it's value? also on log file is ok

Renato

To print all the points that the draw...plot is using, you can:

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15}

\begin{document}
\newcommand{\xmax}{14}
\newcommand{\fmin}{(pi/3)}
\newcommand{\fmax}{(2*pi)}
\begin{tikzpicture}
[domain=\xmax:0, samples=500]
\draw[ultra thick, red] plot (\x, {sin(deg(exp(ln(\fmin)+\x/\xmax*(ln(\fmax)-ln(\fmin)))*\x))} );
\end{tikzpicture}

\pgfmathsetmacro{\step}{\xmax/500}
\foreach \x in {0,\step,...,\xmax} {
\pgfmathparse{sin(deg(exp(ln(\fmin)+\x/\xmax*(ln(\fmax)-ln(\fmin)))*\x))}\pgfmathresult
\par
}

\end{document}


(continuing...)

If you want the output on the log file, you can add (after the par, for example)

 \wlog{x is \x\space and the function \pgfmathresult}


and you'll have in your .log file:

x is 0 and the function 0.0
x is 0.028 and the function 0.02939
x is 0.056 and the function 0.05899
x is 0.084 and the function 0.08878
x is 0.112 and the function 0.11867


For the strange \space, see Space after command with \write

Clearly, to have it only on the log file, use as the loop:

\foreach \x in {0,\step,...,\xmax} {
\pgfmathparse{sin(deg(exp(ln(\fmin)+\x/\xmax*(ln(\fmax)-ln(\fmin)))*\x))}
\wlog{x is \x\space and the function \pgfmathresult}
}


You don't give us much information in your question, so I'm just using some dummy numbers....

\documentclass{article}

\usepackage{tikz}

\begin{document}

\def\x{0.5}
\def\xmax{1}
\def\fmin{1}
\def\fmax{5}

\pgfmathparse{sin(deg(exp(ln(\fmin)+\x/\xmax*(ln(\fmax)-ln(\fmin)))*\x))}\pgfmathresult

\end{document}