General ⇒ String to number

[ihiribar]

Hi!

From the package feynmf i get stringvalues like 'v1' and 'v2'.... 'vN' which represent points in a feynmangraph. I know how to implement \DrawLeftBentLine... my problem is to convert a string into an integernumber.

i want to draw lines by

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\newcommand{\bentline}[2]{
     \ifthenelse{\BehindSubString{v}{#1}<\BehindSubString{v}{#2}}{
           \DrawLeftBentLine
      }{
           \DrawRightBentLine
      }
}

i want to call this by:

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\bentline{v1}{v2} ... .draws the leftbentline
\bentline{v2}{v1} ... draws the rightbentline

But i cannot compare two strings with "<" and ">". i have to convert them to numbers... how do i do this?
Can anybody help?

A minimum example:

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\documentclass{article}
\usepackage{substr,ifthen}

\begin{document}
First: \BehindSubString{v}{v1} %First: 1
Second: \BehindSubString{v}{v2} \\ %Second: 2
Test: \ifthenelse{ 1<2}
        {Even permutation}
        {Odd permutation} %Test: Even permutation
%Next line produces error: 
Result: \ifthenelse{ \BehindSubString{v}{v1}<\BehindSubString{v}{v2}} 
        {Even permutation}
        {Odd permutation}
\end{document}

The error message is

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! Illegal parameter number in definition of \@gtempa.
<to be read again> 
                   2
l.10 ...dSubString{v}{v1}<\BehindSubString{v}{v2}}

P.S.: \BehindSubString is part of the substr package and gets the part behind substring (so the calls above return 1 and 2 respectively but as text not as number)

[ihiribar]

Ok, maybe this is too complicated to do. but is there any other useful way to have a function do something like

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\LeftOrRight{v3}{v5} %writes the word "left"
\LeftOrRight{v1}{v3} %also write the word "left"
\LeftOrRight{v5}{v4} %write the word "right" (because 5>4)
\LeftOrRight{v2}{v1} %write the word "right" (because 2>1)

I believe that this should be possible somehow. But i have no idea how to do it. Please help

[nlct]

You could try something like:

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\documentclass{article}

\usepackage{ifthen}

\def\extract#1#2\relax{#2}
\newcommand{\LeftOrRight}[2]{%
  \ifthenelse{\extract#1\relax<\extract#2\relax}{Left}{Right}%
}

\begin{document}

\LeftOrRight{v3}{v5}
\LeftOrRight{v1}{v3}
\LeftOrRight{v5}{v4}
\LeftOrRight{v2}{v1}

\end{document}

Regards
Nicola Talbot

[ihiribar]

Thank you that was exactly what i needed.