[pstricks] multiplication with multido variable / drawing a lattice

[Brandon Kuczenski]

On Mon, 9 May 2011, Christian Häger wrote:

> Hello,
>
> I want to draw a 2-D lattice (regular array of points) with pstricks. The 
> following example works fine for me
>
> \multido{\nx=-6+1}{13}{
> \multido{\ny=-7+1}{15}{
>   \psdot[dotsize=2.0pt](\numexpr \nx*2,\numexpr \nx*1+\ny*2 )
> }
> }
>
> Unfortunately this is too restrictive and I need a way to multiply the \nx 
> and \ny variables by real numbers, i.e. I want to write something like
>
> \psdot[dotsize=2.0pt](\numexpr \nx*sqrt(3),\numexpr \nx*1.4+\ny*2 )
>
> but this doesn't work. I tried the calc package but couldn't make it work 
> either.
>


You could always use fp.... although I suspect I'm a bit out of date. 
I've never heard of \numexpr.

\usepackage[nomessages]{fp}
\FProot\sqrtthree{3}{2}

...

\multido{\nx=-6+1}{13}{
  \multido{\ny=-7+1}{15}{
     \FPmul\xvar\nx\sqrtthree
     \FPmul\yvar\ny{2}
     \FPmul\tmpvar\nx{1.4}
     \FPadd\yvar\yvar\tmpvar
     \psdot[dotsize=2.0pt](\xvar,\yvar)
  }
}