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8 Expert use of Vole

8.1 InfoVole – getting extra information about a Vole search

8.1-1 InfoVole

InfoVole is the primary info class for Vole. See Reference: Info Functions for a description of info classes in GAP.

The default info level is 0. Most info messages are given at level 2, but some messages are given at other levels, up to level 4.

8.2 Options with the native Vole interface

Most Vole functions support several options, which are implemented with the GAP options system, which is described in the GAP reference manual; see Reference: Options Stack.

In brief, options can be set for a function call by first giving the arguments, then writing a colon, and then assigning values to some or all of the permitted option names. Writing an option name without an explicitly assigned value is a shorthand for assigning the value true to that option. Note that options are passed down to subsequent function calls that are initiated by the original call.

Here is an example of a Vole function call with the option raw set to true:

gap> LoadPackage("vole", false);;

gap> ret := Vole.Intersection(AlternatingGroup(6), PGL(2,5) : raw := true);
rec( cosetrep := (), group := Group([ (3,5)(4,6), (2,3,4,6,5), (1,2,6)(3,4,5)
     ]),
  raw := rec( canonical := fail, rbase_branches := [ 1, 2, 3 ],
      search_fix_order := [ 1, 2, 3, 6, 5, 4 ],
      sols := [ [  ], [ 1, 2, 5, 6, 3, 4 ], [ 1, 3, 4, 6, 2, 5 ],
          [ 2, 6, 4, 5, 3, 1 ] ],
      stats := rec( bad_canonical := 0, bad_iso := 3, equal_canonical := 0,
          gap_callbacks := rec( begin := 2, canonicalmin_time := 0,
              changed := 24, check := 11, compare := 0, fixed := 38,
              image := 0, is_group := 0, name := 0, rBaseFinished := 2,
              refiner_time := 40, restore_state := 24, save_state := 24 ),
          good_iso := 4, improve_canonical := 0, refiner_calls := 64,
          search_nodes := 13, trace_fail_nodes := 0, vole_time := 136 ) ),
  sols := [ (), (3,5)(4,6), (2,3,4,6,5), (1,2,6)(3,4,5) ], time := 220 )
gap> ret.group = PSL(2,5);
true

Note that the option raw can also be set to true by simply giving the name raw. Therefore the following line can be used in place of the one above:

gap> ret := Vole.Intersection(AlternatingGroup(6), PGL(2,5) : raw);;

8.2-1 Supported options

• raw: true or (default) false:

  • If true, then rather than returning an object as documented, the function returns a record that contains detailed information about the execution and result of the graph backtracking algorithm that was executed. The meaning of this information is not yet documented, sorry.

  • Not all Vole functions support this option, although most do.

• points: a non-negative integer or (default) infinity:

  • This option can be used in place of the constraint Constraint.LargestMovedPoint(points); see Constraint.LargestMovedPoint (BacktrackKit: Constraint.LargestMovedPoint).

  • Note that for relevant functions that accept constraints, an integer argument is interpreted as an instance of a ‘largest moved point’ constraint, which achieves the same affect as this option more simply.

gap> D := PetersenGraph();;
gap> constraint := Constraint.Stabilise(D, OnDigraphs);;
gap> G := VoleFind.Group(constraint : points := DigraphNrVertices(D));;
gap> [NrMovedPoints(G), TransitiveIdentification(G)];
[ 10, 13 ]

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