Hcfyk

I am trying to draw a tree using tikzpicture like this:

begin{tikzpicture}

    tikzstyle{node}=[circle, fill=blue!25, minimum size=0.1 cm];

    foreach ilayer in {0,...,3} {

        tikzmath {nnodes = 3 ^ ilayer; }

        tikzmath {leftnum = 1 - floor(nnodes / 2) - 1; }

        tikzmath {rightnum = nnodes - floor(nnodes / 2) - 1; }

        foreach isibling in {leftnum,...,rightnum} {                

            tikzmath {d = 3 ^ (- ilayer) * 15; }

            tikzmath {x = isibling * d; }

            tikzmath {y = - ilayer * 2; }

            node[node] (node_ilayer_isibling) at (x cm, y cm) {isibling};

        }

    }

end{tikzpicture}

I get the tree like the following picture. The texts are nodes' isibling within each layer. Most nodes are integers, but all leftmost nodes are not.

You could just tell TikZ explicitly that you want an integer.

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{math}

begin{document}

begin{tikzpicture}

    tikzset{mynode/.style={circle, fill=blue!25, minimum size=0.1 cm}}

    foreach ilayer in {0,...,3} {

        tikzmath {nnodes = 3 ^ ilayer; }

        tikzmath {leftnum = int(1 - floor(nnodes / 2) - 1); }

        tikzmath {rightnum = nnodes - floor(nnodes / 2) - 1; }

        foreach isibling in {leftnum,...,rightnum} {                

            tikzmath {d = 3 ^ (- ilayer) * 15; }

            tikzmath {x = isibling * d; }

            tikzmath {y = - ilayer * 2; }

            node[mynode] (node_ilayer_isibling) at (x cm, y cm) {isibling};

        }

    }

end{tikzpicture}

end{document}

Or

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{math}

begin{document}

begin{tikzpicture}

    tikzset{mynode/.style={circle, fill=blue!25, minimum size=0.1 cm}}

    foreach ilayer in {0,...,3} {

        tikzmath {int nnodes,leftnum,rightnum;

            nnodes = 3 ^ ilayer;

            leftnum = 1 - floor(nnodes / 2) - 1; 

        rightnum = nnodes - floor(nnodes / 2) - 1; }

        foreach isibling in {leftnum,...,rightnum} {                

            tikzmath {d = 3 ^ (- ilayer) * 15; 

            x = isibling * d; 

            y = - ilayer * 2; }

            node[mynode] (node_ilayer_isibling) at (x cm, y cm) {isibling};

        }

    }

end{tikzpicture}

end{document}

In principle you do not need the math library here.

documentclass[tikz,border=3.14mm]{standalone}

begin{document}

begin{tikzpicture}

    tikzset{mynode/.style={circle, fill=blue!25, minimum size=0.1 cm}}

    foreach ilayer [evaluate=ilayer as nnodes using {int(3 ^ ilayer)},

    evaluate=nnodes as leftnum using {int(1 - floor(nnodes / 2) - 1)},

    evaluate=nnodes as rightnum using {int(nnodes - floor(nnodes / 2) - 1)}]

    in {0,...,3} {

        foreach isibling 

        [evaluate=ilayer as d using {3 ^ (- ilayer) * 15},

        evaluate=isibling as x using {isibling * d},

        evaluate=ilayer as y using {- ilayer * 2}]

        in {leftnum,...,rightnum} {                

            node[mynode] (node_ilayer_isibling) at (x cm, y cm) 

            {isibling};

        }

    }

end{tikzpicture}

end{document}

As @marmot said you do not need tikzmath here, but if you use it you can do it in more efficient way :

• You can have a single tikzmath command with loops inside it.


• You can declare your integer variables as int so you do not need to do int() afterward.


• As nnodes is odd you do not need separate rightnum and leftnum as rightnum = - leftnum;


• Why you use 1-floor(nnodes/2)-1 in place of -floor(nnodes/2) ?


• The value d can be calculated in the outer loop.


• Instead of using x=isibling*d you can say [x=d cm] and then use isibling asx. And in the same way y can be replaced by ilayer using [y=-2cm].

So here is my proposal :

documentclass[tikz,border=7pt]{standalone}

usetikzlibrary{math}

begin{document}

begin{tikzpicture}

  tikzstyle{node}=[circle, fill=blue!25, minimum size=0.1 cm];

  tikzmath{

    int ilayer,nnodes,rightnum,isibling;

    nnodes = 1;

    for ilayer in {0,...,3}{

      rightnum = (nnodes-1)/2;

      d = 15/nnodes;

      for isibling in {-rightnum,...,rightnum}{

        {

          path[x=d cm,y=-2cm]

            node[node] (node_ilayer_isibling) at (isibling, ilayer) {isibling};

        };

      };

      nnodes = 3*nnodes;

    };

  }

end{tikzpicture}

end{document}