Example: Two tank system

graph G {
    node[shape=doublecircle, fixedsize=true, width=0.4];
    graph [style="rounded corners"];
    subgraph cluster0 {
    	style = "red, fill=blue!20,rounded corners";    	
    	label = "Tank 1";
    	node [texmode="math"]
    	c_1--q_L; c_1--h_1;
        c_2--q_P;	c_2--h_1;
    	c_3--q_L; c_3--q_P; c_3--dh_1; 
    	d_4--dh_1;d_4--h_1;
    	dh_1 [label="\\dot{h}_1"];
    }
    
    subgraph cluster1{
	label = "Pipe";  
	node [texmode="math"]
	c_5--h_1; c_5--q_12;
	q_12 [label="q_{12}"];
    }
    
    c_5--h_2;
    c_3--q_12;
    c_6--q_12;
    
    subgraph cluster2{
    	label = "Tank 2";
    	node [texmode="math"]
    	c_6--dh_2;c_6--q_2;
    	d_7--dh_2; d_7--h_2;
    	c_8--h_2;c_8--q_2;
    	c_m--q_2;
    	dh_2 [label="\\dot{h}_2"];
    }
}