# [pstricks] Nodes at the ends of a tangent line

Akos Valentinyi A.Valentinyi at soton.ac.uk
Mon Jan 23 16:59:03 CET 2006

Hi,

I do regularly a type of graph (see below) where the
tangent line to a curve extends to both the Y and the
X axis.

Right now I am doing in a complicated way. However,
if \plotTangent would give me two nodes, one
at each end of the tangent line, this could
be simplified. This is basically having
the slope of the tangent line in terms of two
nodes.

Any chance for that?

Thanks

Akos

\documentclass[12pt]{article}
\usepackage{amsmath,amsbsy}

\begin{document}
\setlength{\pslinewidth}{2pt}

\psset{plotpoints=200,xunit=0.5in,yunit=0.5in}
\psset{PointName=none,PointSymbol=none}

\Large
\begin{pspicture}(-1.5,-1.5)(11.5,10)
\psaxes[linewidth=0.5\pslinewidth,labels=none,ticks=none]{->}(0,0)(11,10)
\pnode(0,0){O}\pnode(11,0){X}\pnode(0,10){Y}
\def\F{8.5 x 0.75 exp div}
\def\Slope{-8.5 0.75 mul x 1.75 exp div}
\psplot{1}{10}{\F}
\def\xA{3.25}
\pstGeonode(!\xA\space /x \xA\space def \F){T}
\pstGeonode(!1 /x 1 def \F){A}
\pstGeonode(!4 /x 1 def \F\space /x \xA\space def \Slope\space -1 mul 4 1 sub mul sub){B}
\pstTranslation{A}{B}{T}[B'']
\pstInterLL{T}{B''}{O}{X}{B'}
\pstInterLL{T}{B''}{O}{Y}{A'}
\pstLineAB{A'}{B'}
\qdisk(T){2\pslinewidth}
\nput{45}{T}{\Large $O$}
\pstGeonode(!0 /x \xA\space def \F){C_2}
\pstGeonode(\xA,0){C_1}
\psline[linewidth=0.5\pslinewidth,linestyle=dashed](C_1)(T)(C_2)
\nput[nodesep=2ex]{270}{C_1}{$c_1$}
\nput[nodesep=2ex]{180}{C_2}{$c_2$}
\end{pspicture}
\endTeXtoEPS

\end{document}

******************************************************************
Akos Valentinyi
Economics Division
School of Social Sciences
University of Southampton
Highfield                                   Phone: +44 23 80592536
Southampton SO17 1BJ                          Fax: +44 23 80593858
United Kingdom                         http://www.soton.ac.uk/~av2
******************************************************************