%% 
%%  A DANTE-Edition example
%% 
%%  Example 36-00-42 on page 785.
%% 
%%  Copyright (C) 2011 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{article}
\pagestyle{empty}
\setlength\textwidth{201.70511pt}
\setlength\parindent{0pt}

\usepackage{pst-plot,multido}
\usepackage[nomessages]{fp}
\newwrite\DataFileA
\newwrite\DataFileB
%
\newcommand{\DataFileNameA}{MyCurveA.dat}
\newcommand{\DataFileNameB}{MyCurveB.dat}
%
\def\Xpsz{6}
\def\Ypsz{6}
\newcommand{\PerCalc}[2]{%
  \def\ix{#1}\def\iy{#2}%
  \FPeval{\iY}{\Ypsz * \iy / (\iy + 1.0)}  % Calculates Y-coordinate
  \FPeval{\iX}{(\Ypsz - \iY)* \ix / \Xpsz} % Calculates X-coordinate
}% End perspective calculate


\begin{document}
\begin{pspicture}(-6,0)(6,6)
  \multido{\I=-6+1}{13}{\psline(0,6)(\I,0)}
  % The horizontal perspective grid
  \multido{\IR=0+1}{13}{%
    \PerCalc{-6.0}{\IR}
    \FPneg{\iXX}{\iX}                         %
    \psline[linecolor=red](\iXX,\iY)(\iX,\iY)}% End of the horizontal grid
%
  \immediate\openout\DataFileA=\DataFileNameA
  \immediate\openout\DataFileB=\DataFileNameB
%
  \multido{\IRx=0+1}{90}{%
    \FPeval{\Ry}{ (\IRx * \IRx) / 30.0 }   % Defines the quadratic
    \PerCalc{\IRx}{\Ry}
    \immediate\write\DataFileA{(\iX,\iY)}
    \FPneg{\iXX}{\iX} %
    \immediate\write\DataFileB{(\iXX,\iY)}}
%
  \immediate\closeout\DataFileA
  \immediate\closeout\DataFileB
%
  \readdata{\MyCurve}{\DataFileNameA}
  \dataplot[plotstyle=curve,%
	showpoints=true,%
	linecolor=green,linewidth=1.5pt]{\MyCurve}

  \readdata{\MyCurve}{\DataFileNameB}
  \dataplot[plotstyle=curve,%
	showpoints=true,%
	linecolor=blue,linewidth=1.5pt]{\MyCurve}
\end{pspicture}
\end{document}