This function returns the induced subgraph of a (hyper)graph on a specified set of vertices. This function enables the user to create subgraphs of the original (hyper)graph.
The default option is for the ring of the induced subgraph to contain only variables in L. Then the current ring must be changed before working with the induced subgraph. We use this setup to avoid having a lot of isolated vertices in the induced (hyper)graph. However, one can set the option OriginalRing to true if one wants to give the induced (hyper)graph the same ring as the original (hyper)graph.
Note: Since Graph is a Type of HyperGraph, inducedHyperGraph can be used for graphs, but the output is a HyperGraph. If one prefers to have a graph returned instead, use inducedGraph.
i1 : R = QQ[a,b,c,d,e]; |
i2 : G = graph {a*b,b*c,c*d,d*e,e*a} -- graph of the 5-cycle
o2 = Graph{edges => {{a, b}, {b, c}, {c, d}, {a, e}, {d, e}}}
ring => R
vertices => {a, b, c, d, e}
o2 : Graph
|
i3 : H1 = inducedHyperGraph(G,{b,c,d,e})
o3 = HyperGraph{edges => {{b, c}, {c, d}, {d, e}}}
ring => QQ[b..e]
vertices => {b, c, d, e}
o3 : HyperGraph
|
i4 : H2 = inducedHyperGraph(G,{a,b,d,e})
o4 = HyperGraph{edges => {{a, b}, {a, e}, {d, e}}}
ring => QQ[a..b, d..e]
vertices => {a, b, d, e}
o4 : HyperGraph
|
i5 : use ring H1 o5 = QQ[b..e] o5 : PolynomialRing |
i6 : inducedHyperGraph(H1,{c,d,e})
o6 = HyperGraph{edges => {{c, d}, {d, e}}}
ring => QQ[c..e]
vertices => {c, d, e}
o6 : HyperGraph
|
i7 : use ring G o7 = R o7 : PolynomialRing |
i8 : inducedHyperGraph(G,{b,c,d,e},OriginalRing=>true) --H1 but in bigger ring
o8 = HyperGraph{edges => {{b, c}, {c, d}, {d, e}}}
ring => R
vertices => {a, b, c, d, e}
o8 : HyperGraph
|
Equivalently, one can use changeRing to move the induced hypergraph back into the original ring.
i9 : R = QQ[a,b,c,d,e]; |
i10 : G = graph {a*b,b*c,c*d,d*e,e*a} -- graph of the 5-cycle
o10 = Graph{edges => {{a, b}, {b, c}, {c, d}, {a, e}, {d, e}}}
ring => R
vertices => {a, b, c, d, e}
o10 : Graph
|
i11 : H = inducedHyperGraph(G,{b,c,d})
o11 = HyperGraph{edges => {{b, c}, {c, d}}}
ring => QQ[b..d]
vertices => {b, c, d}
o11 : HyperGraph
|
i12 : changeRing(H,R,{b,c,d})
o12 = HyperGraph{edges => {{c, d}, {b, c}} }
ring => R
vertices => {a, b, c, d, e}
o12 : HyperGraph
|
The object inducedHyperGraph is a method function with options.