I have the following code, which produces no errors in the log files:
\documentclass[border=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{width=14cm,compat=1.14, label style={font=\huge}, tick label style={font=\huge}}
\usepgfplotslibrary{fillbetween}
\begin{document}
\pgfmathdeclarefunction{lgamma}{1}{%
\pgfmathparse{ln(2.506628274631*sqrt(1/#1) + 0.20888568*(1/#1)^(1.5) + 0.00870357*(1/#1)^2.5 - (174.2106599*(1/#1)^3.5)/25920 - (715.6423511*(1/#1)^4.5)/1244160)*(-ln(1/#1)-1)*#1}
}
\pgfmathdeclarefunction{chisq}{1}{%
\pgfmathparse{exp((0.5*#1-1.0)*ln(x)-0.5*x-lgamma(0.5*#1)-#1*0.5*0.693147180559945)}%
}
\begin{tikzpicture}
\begin{axis}[
no markers, domain=0.01:3.5, samples=300,
axis x line=bottom, axis y line=left,
every axis y label/.style={at=(current axis.above origin),anchor=south},
every axis x label/.style={at=(current axis.right of origin),anchor=west},
height=5cm, width=14cm,
xtick={0.01, 3.5}, ytick=\empty,
enlargelimits=false, clip=false, axis on top,
xticklabels={0, $\infty$}, % so do it manually instead
]
\addplot [very thick,red, name path=f] {chisq(1)};
% \path[name path=axis](axis cs:0.01,0) -- (axis cs:3.5,0);
%\addplot[thick, color=red, fill=red, fill opacity=0.5] fill between [of=f and axis, soft clip={domain=0.01:3.5},];
\end{axis}
\end{tikzpicture}
\end{document}
However, it produces a blank page when I try to use pdflatex. Why? How can I get my chisq(1) plot to show, and the area between f(x) and the x-axis to be shaded in red?