# How plot a function using only variables not their values?

How can I plot a diagram like this? • You will have to provide more information and effort. This is a Question-and-Answer site, not a "Draw this for me" site. Show us, what you tried, where you got stuck and we will be happy to help you. Also, i don't really understand the question. What do you mean by 'using only variables not their values'? Do you mean you don't want to calculate the function beforehand. This is possible, using for example pgfplots. – pschulz Jan 27 '17 at 9:48

Here is a starting point using tikz. For more sophisticated/real plots there are specialized packages, but this seems to be an overkill for a simple illustration. \documentclass[border=2mm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[xscale=2,yscale=4] % scale 1x1 drawing as needed
\draw[domain=0:-180,samples=100] plot ({cos(\x)},{sin(\x)}); % lower half of circle
\draw (-1,-1) -- (1,-1); % bottom line
\draw[dashed] (-1,-1) node[below]{\scriptsize LSL}    -- (-1,0);
\draw[dashed] ( 0,-1) node[below]{\scriptsize Target} -- ( 0,0);
\draw[dashed] ( 1,-1) node[below]{\scriptsize USL}    -- ( 1,0);
\foreach \y/\l in {-1/0,-0.8/20,-0.6/40,-0.4/60,-0.2/80,0/100}
\draw (-1,\y) node[left]{\scriptsize\l};
\draw (-1.4,-0.5) node[rotate=90] {Taguchi Loss};
\end{tikzpicture}
\end{document}

• Thanks a lot. I had many more graphs similar to this one, now I can use this example to generate others. Thanks. – amin seyedhaeri Jan 28 '17 at 11:17