LaTeX Trellis Diagrams for STBCs

Question

I recently had to draw multiple trellises for space-time block codes (first introduced in this paper; the open-access version is here). I'd like to share the code with you here, so that the work doesn't have to be done twice.

As you see, I created a new command for plotting a trellis, where you can add the number of states, the PSK order, and the x- and y-distance between points as arguments:

\documentclass[a4paper]{article}

\usepackage{pst-plot,pst-sigsys}
\usepackage[nomessages]{fp}

\newcommand{\trellis}[4]{
  \def \STATES {#1}
  \def \PSK {#2}
  \def \XDISTANCE {#3}
  \def \YDISTANCE {#4}
  \FPupn\NGROUPS{\STATES{} \PSK{} div 0 trunc}
  \multido{\ryA=0+-\YDISTANCE,\nA=1+1}{\STATES}{%
    \dotnode(0,\ryA){dotA\nA}
    \dotnode(\XDISTANCE,\ryA){dotB\nA}
  }
  \multido{\nG=1+1,\nOffset=1+\PSK}{\NGROUPS}{%
    \multido{\nStart=\nG+\NGROUPS}{\PSK}{%
      \multido{\nArrows=\nOffset+1}{\PSK}{%
        \ncline{dotA\nStart}{dotB\nArrows}
      }
    }
  }
}

\begin{document}
  \begin{pspicture}[showgrid=true](0,0)(12,-20)
    \rput(0,0){\trellis{4}{4}{1.}{1}}
    \rput(3,0){\trellis{16}{4}{1.5}{1}}
    \rput(6,0){\trellis{8}{8}{2.25}{2.25}}
  \end{pspicture}
\end{document}

Answer 1

You have a lot of trailing spaces which move your image to the right. If you are not sure where to place a % at the line end then do it for every line:

\newcommand{\trellis}[4]{%
  \def \STATES {#1}%
  \def \PSK {#2}%
  \def \XDISTANCE {#3}%
  \def \YDISTANCE {#4}%
  \FPupn\NGROUPS{\STATES{} \PSK{} div 0 trunc}%
  \multido{\ryA=0+-\YDISTANCE,\nA=1+1}{\STATES}{%
    \dotnode(0,\ryA){dotA\nA}
    \dotnode(\XDISTANCE,\ryA){dotB\nA}
  }%
  \multido{\nG=1+1,\nOffset=1+\PSK}{\NGROUPS}{%
    \multido{\nStart=\nG+\NGROUPS}{\PSK}{%
      \multido{\nArrows=\nOffset+1}{\PSK}{%
        \ncline{dotA\nStart}{dotB\nArrows}
      }%
    }%
  }%
}

PSTricks macros itself kill all glue, so the last % three are not needed. But it doesn't hurt ...

and I suppose that you do not need the fppackage. Try \numexpr

\multido{\nG=1+1,\nOffset=1+\PSK}{\numexpr\STATES/\PSK}{%
  \multido{\nStart=\nG+\numexpr\STATES/\PSK}{\PSK}{%