[pstricks] Sieve

[Herbert Voss]

David Arnold schrieb:
> Nice solution. I wound up with following. Brute force, but it worked.

you can calculate anything in PS ...

Herbert

\documentclass{article}
\usepackage{pstricks-add}
\begin{document}

\pstVerb{
 /prime? {
  /n exch def
  n 1 eq {false} { % 1 is not prime
    n 2 mod 0 eq {n 2 eq} {
      /divide? false def
      3 2 n sqrt {
        n exch div dup ceiling eq {/divide? true def exit} if
      } for
      divide? not } ifelse } ifelse
} bind def
}
\makeatletter
\begin{pspicture}(0,0)(10,-10)
\psgrid[subgriddiv=1,gridlabels=0pt]
\multido{\iA=2+1}{99}{%
  \rput(! \iA\space 2 sub 10 mod /xVal ED
          \iA\space 2 sub 10 div cvi neg /yVal ED
          \iA\space prime? not {
            gsave xVal yVal \tx at ScreenCoor translate
            0 0 moveto 1 -1 \tx at ScreenCoor lineto
            0 -1 \tx at ScreenCoor moveto 1 0 \tx at ScreenCoor lineto
            1 setlinewidth 1 0 0 setrgbcolor stroke grestore } if
          xVal 0.5 add yVal 0.5 sub ){\iA}}
\end{pspicture}

\end{document}


Herbert