mjhjmtu

Is it possible to use the node distance as a variable while expressing coordinates of new nodes with Calc and Positioning libraries? What I want to have is everything within a single piece of code for tikz picture.

This is what I have now.

documentclass[12pt, a4paper]article
usepackagetikz
usetikzlibraryautomata, positioning, arrows,calc

begindocument
begintikzpicture[>=stealth',shorten >=0.5pt,auto,node distance=2cm,semithick,on grid]

 tikzstyleevery state=[minimum size=20pt, fill=none,draw=black]
 node[state,label=center:$a$,inner sep=0pt] (a) ;
 node[state,label=center:$b$] (b) at ($(a) + sqrt(1/3)*4*(0:1cm) $) ;
 node[state,label=center:$c$] (c) at ($(a) + sqrt(1/3)*4*(-60:1cm)$) ;

 path[->] (a) edge node $1$ (b)
 (c) edge node[right] $1$ (b)
 (b) edge [loop right] node[above] $0,1$ (b);
 path[shorten <=0.5pt,<->] (a) edge node[left]$0$ (c);

endtikzpicture
enddocument

I would like to be able to change the below expression with something like:

$(a) + sqrt(1/3)*2*(1:nodedistance)$

Then if I would be copying the code elsewhere, such as a presentations, I would be able to change all these distances at once. Is that possible? If not, introducing a variable in the first line of the TikZ code, and using it afterwards instead the "nodedistance", would also do.

Sorry if it's a dull question, I'm pretty new to TikZ.

AFAIK you cannot simply read off the value of /tikz/node distance. However, in this great answer by @Jake there is a simple way to amend node distance by a pgf key that you can use.

documentclass[12pt, a4paper]article
usepackagetikz
usetikzlibraryautomata, positioning, arrows,calc
tikzsetnode distance/.append code=
 pgfkeyssetvalue/tikz/node distance value#1
 
begindocument
begintikzpicture[>=stealth',shorten >=0.5pt,auto,node
distance=2cm,semithick,on grid,
every state/.style=minimum size=20pt, fill=none,draw=black]
 node[state,label=center:$a$,inner sep=0pt] (a) ;
 node[state,label=center:$b$] (b) at ($(a) + sqrt(4/3)*(0:pgfkeysvalueof/tikz/node distance value) $) ;
 node[state,label=center:$c$] (c) at ($(a) + sqrt(4/3)*(-60:pgfkeysvalueof/tikz/node distance value)$) ;

 path[->] (a) edge node $1$ (b)
 (c) edge node[right] $1$ (b)
 (b) edge [loop right] node[above] $0,1$ (b);
 path[shorten <=0.5pt,<->] (a) edge node[left]$0$ (c);
endtikzpicture
enddocument

You can create a macro defnodedistance1cm at the begining of the tikzpicture . Later if needed this macro could be redefined .

documentclass[12pt, a4paper]article
usepackagetikz
usetikzlibraryautomata, positioning, arrows,calc

begindocument
begintikzpicture[>=stealth',shorten >=0.5pt,auto,semithick,on grid]

defnodedistance1cm % <------------ 

 tikzstyleevery state=[minimum size=20pt, fill=none,draw=black]
 node[state,label=center:$a$,inner sep=0pt] (a) ;
 node[state,label=center:$b$] (b) at ($(a) + sqrt(1/3)*4*(0:nodedistance) $) ;
 node[state,label=center:$c$] (c) at ($(a) + sqrt(1/3)*4*(-60:nodedistance)$) ;

 path[->] (a) edge node $1$ (b)
 (c) edge node[right] $1$ (b)
 (b) edge [loop right] node[above] $0,1$ (b);
 path[shorten <=0.5pt,<->] (a) edge node[left]$0$ (c);

endtikzpicture

begintikzpicture[>=stealth',shorten >=0.5pt,auto,semithick,on grid]

defnodedistance2cm % <----------------

 tikzstyleevery state=[minimum size=20pt, fill=none,draw=black]
 node[state,label=center:$a$,inner sep=0pt] (a) ;
 node[state,label=center:$b$] (b) at ($(a) + sqrt(1/3)*4*(0:nodedistance) $) ;
 node[state,label=center:$c$] (c) at ($(a) + sqrt(1/3)*4*(-60:nodedistance)$) ;

 path[->] (a) edge node $1$ (b)
 (c) edge node[right] $1$ (b)
 (b) edge [loop right] node[above] $0,1$ (b);
 path[shorten <=0.5pt,<->] (a) edge node[left]$0$ (c);

endtikzpicture
enddocument