Adjusting width of clusters

Help
1

How can I adjust the width of Cluster_2 to match the width of cluster_1

digraph {
rankdir=LR

subgraph “cluster_MT”{

    subgraph "cluster_B1" {
      subgraph clusterI2{
        peripheries=0 // no surrounding box
        margin=0      // reduce vertical space
        "B1_invis"[shape=point style=invis width=0.01]  // pin ignored by dot  pin=true]
      }
      label = "Cluster_2"
    } 

    subgraph "cluster_A1" {
      "A1_invis"[shape=point style=invis ]  // pin ignored by dot  pin=true]
        
      "A1"[label="Node 1", shape=rectangle]
      label = "Cluster_1"

      subgraph "cluster_A2"{
        A2[label="Node 2" shape=rectangle]  
        label = "Subcluster_1"
      }
    }

label = "Big Box"

}

}

2

Short answer: no “simple” way to do this (e.g. setting height and/or width on clusters is ignored)

However, it can be done.
For a one-time graph, you can produce an output file in xdot format (DOT | Graphviz), and hand-edit the bb (bb | Graphviz) or of the clusters that need to grow or the width of the node that needs to grow. Then feed that edited file into neato -n … (FAQ | Graphviz)
Surprisingly easy since you are editing a text file. See below.

If you want something that can be programmatically “fixed”, a python, gvpr (https://www.graphviz.org/pdf/gvpr.1.pdf), or … program can find the bb entry of the clusters (after running dot myFile.gv > myFile.dot), calculate the widest width, and then apply that width to the other clusters or nodes as appropriate. That is how I manually came to modify your file:

digraph {
  rankdir=LR

  subgraph “cluster_MT”{

    subgraph "cluster_B1" {
      subgraph clusterI2{
        peripheries=0 // no surrounding box
        margin=0      // reduce vertical space
        // width in inches, based on bb in points of other cluster
        "B1_invis" [shape=none Xstyle=invis label="" fixedsize=true  width=1.525 height=.02]  
      }
      label = "Cluster_2"
    }

    subgraph "cluster_A1" {
      "A1_invis"[shape=point style=invis ]
      "A1" [label="Node 1", shape=rectangle]
      label = "Cluster_1"

      subgraph "cluster_A2"{
        A2 [label="Node 2" shape=rectangle]
        label = "Subcluster_1"
      }
    }

    label = "Big Box"
  }
}
digraph {
  rankdir=LR

  subgraph “cluster_MT”{

    subgraph "cluster_B1" {
      subgraph clusterI2{
        peripheries=0 // no surrounding box
        margin=0      // reduce vertical space
        // width in inches, bb in points
        "B1_invis" [shape=none Xstyle=invis label="" fixedsize=true  width=1.525 height=.02]  
      }
      label = "Cluster_2"
    }

    subgraph "cluster_A1" {
      "A1_invis"[shape=point style=invis ]
      "A1" [label="Node 1", shape=rectangle]
      label = "Cluster_1"

      subgraph "cluster_A2"{
        A2 [label="Node 2" shape=rectangle]
        label = "Subcluster_1"
      }
    }
    label = "Big Box"
  }
}

Giving:
sameWidthClusters1