I need some help!

[Isaiah Shavitt]

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Thanks to Denis Girou for the prompt response to my request for help.

I did get useful information from the response; I looked in the PS 
header file produced by PST and found many definitions that I wanted 
to know about.

I have some specific questions which may perhaps be answered easily.
Below I copy a sample macro from my macro collection, on which I can 
illustrate some of my problems.  This macro draws a line segment 
from point (#2,#3) to (#4,#5) and puts an arrow pointing to (#4,#5) 
with the CENTER of the arrow (not its tip) #1 of the distance from 
(#2,#3) to (#4,#5) (default #1=0.5), preceded by some generic 
settings and followed by use examples:

\documentclass[12pt]{book}
\usepackage{pstricks}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{ifthen}
\textwidth 6.5in%
\textheight 9.0in%
\topmargin -0.35in%
\oddsidemargin 0in%
\evensidemargin 0in%
\lineskip=3pt minus 1pt%
\lineskiplimit=2pt%
\parskip 0.2in%
\parindent 0.25in%

\psset{arrowsize=2pt 4,dotsep=2pt}
\newlength{\xl}\newlength{\yl}\newlength{\xc}\newlength{\yc}
\def\ArrowShift{0.15 } % Distance from the center of the arrow to its tip
\SpecialCoor

\newcommand{\dline}[5][0.5]{
\qline(#2,#3)(#4,#5)
\pssetlength{\xl}{#4}\psaddtolength{\xl}{-#2}   % x-component of vector
\pssetlength{\yl}{#5}\psaddtolength{\yl}{-#3}   % y-component of vector
\pssetlength{\xc}{#2}\psaddtolength{\xc}{#1\xl} % x-coor of arrow center
\pssetlength{\yc}{#3}\psaddtolength{\yc}{#1\yl} % x-coor of arrow center
\psline{->}(\xc,\yc)
 (!/Mydict 10 dict def Mydict begin
   /Xl #4 #2 sub def /Yl #5 #3 sub def
   /Xc #1 #4 mul 1 #1 sub #2 mul add def
   /Yc #1 #5 mul 1 #1 sub #3 mul add def
   Yl Xl atan dup cos \ArrowShift mul Xc add
   exch sin \ArrowShift mul Yc add end)
}

\begin{document}

\begin{center}
\begin{pspicture}(-0.5,0)(1.5,2)
\dline{0}{0}{0}{2}
\dline{1}{2}{1}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.3,2)
\dline{0}{0}{0.8}{2}
\dline{1.8}{2}{1}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.3,2)
\dline{0.8}{0}{0}{2}
\dline{1}{2}{1.8}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.5,2)
\dline{0}{1.5}{2}{1.5}
\dline{2}{0.5}{0}{0.5}
\end{pspicture}
\end{center}

\begin{center}
\begin{pspicture}(-0.5,0)(1.5,2)
\dline[0.7]{0}{0}{0}{2}
\dline[0.3]{1}{2}{1}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.3,2)
\dline[0.7]{0}{0}{0.8}{2}
\dline[0.3]{1.8}{2}{1}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.3,2)
\dline[0.7]{0.8}{0}{0}{2}
\dline[0.3]{1}{2}{1.8}{0}
\end{pspicture}
\qquad
\begin{pspicture}(-0.5,0)(2.5,2)
\dline[0.7]{0}{1.5}{2}{1.5}
\dline[0.3]{2}{0.5}{0}{0.5}
\end{pspicture}
\end{center}

\end{document}

The macro works well, but note the following points:

1. It computes the coordinates of the arrow center twice, first in LaTeX 
   with the \pssetlength, \psaddtolength commands, giving (\xc,\yc) which 
   define the starting point in the \psline command, and second in the ps 
   code to help in the calculation of the arrow tip position.  I have not 
   found a way of using the numerical values of \Xl, \Yl, \Xc, \Yc in the  
   ps code.

2. I used the LaTeX definition \newcommand{\dline}[5][0.5]{...} instead 
   of the TeX form \def\dline[#1](#1,#2)(#3,#4){...} because I don't know 
   how to have an optional argument in the TeX \def.  But as a result, 
   I cannot use the PST convention for specifying coordinate pairs (x,y) 
   and have to use {x}{y} instead.

Any comments about the above code will be appreciated.  I have other 
questions, but will leave them to another posting.

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Isaiah Shavitt
Professor Emeritus
Department of Chemistry           Telephone: 614-292-1668
The Ohio State University         Fax:       614-292-1685
Columbus, OH 43210-1185           E-mail: shavitt at chemistry.ohio-state.edu
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