digraph G {
  graph [rankdir=LR];

  subgraph cluster_P1 {
    a;
    share_a[label="share"];
    a1;
    b1;
    subgraph cluster_mul1 {
      "*1"[label="*"];
      share1[label="share"];
      recombine1[label="recombine"];
    }
    output1;
  }

  subgraph cluster_P2 {
    b;
    share_b[label="share"];
    a2;
    b2;
    subgraph cluster_mul2 {
      "*2"[label="*"];
      share2[label="share"];
      recombine2[label="recombine"];
    }
    output2;
  }

  subgraph cluster_P3 {
    a3;
    b3;
    subgraph cluster_mul3 {
      "*3"[label="*"];
      share3[label="share"];
      recombine3[label="recombine"];
    }
    output3;
  }

  a -> share_a;
  share_a -> a1;
  share_a -> a2;
  share_a -> a3;

  b -> share_b;
  share_b -> b1;
  share_b -> b2;
  share_b -> b3;

  a1 -> "*1";
  b1 -> "*1";

  a2 -> "*2";
  b2 -> "*2";

  a3 -> "*3";
  b3 -> "*3";

  "*1" -> share1;
  "*2" -> share2;
  "*3" -> share3;

  share1 -> recombine1;
  share1 -> recombine2;
  share1 -> recombine3;

  share2 -> recombine1;
  share2 -> recombine2;
  share2 -> recombine3;

  share3 -> recombine1;
  share3 -> recombine2;
  share3 -> recombine3;

  recombine1 -> output1;
  recombine2 -> output2;
  recombine3 -> output3;
}