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Annotation of OpenXM_contrib/PHC/Ada/Root_Counts/Symmetry/permutations.ads, Revision 1.1.1.1

1.1       maekawa     1: with Standard_Integer_Vectors;
                      2:
                      3: package Permutations is
                      4:
                      5: -- DESCRIPTION :
                      6: --   This package defines the type Permutation.
                      7:
                      8:   type Permutation is new Standard_Integer_Vectors.Vector;
                      9:   type Link_to_Permutation is new Standard_Integer_Vectors.Link_to_Vector;
                     10:
                     11:   -- DESCRIPTION :
                     12:   --   A permutation p defines the image of i -> p(i).
                     13:   --   As also negative entries are alowed, sign permutations
                     14:   --   will be modelled as follows:
                     15:   --     let perm = (1 3 -2), applied to F=(f1,f2,f3):
                     16:   --     perm*F = (f1,f3,-f2).
                     17:
                     18:   function Is_Permutation ( p : Permutation ) return boolean;
                     19:
                     20:   -- DESCRIPTION :
                     21:   --   Checks whether the vector p models a permutation:
                     22:   --    p(i) /= p(j) and p(i) /= -p(j), for all i /= j and
                     23:   --    -p'last <= p(i) <= p'last.
                     24:
                     25:   function Equal ( p1,p2 : Permutation ) return boolean;
                     26:
                     27:   -- DESCRIPTION :
                     28:   --   Returns true if both permutations are equal.
                     29:
                     30:   function "*" ( p1,p2 : Permutation ) return Permutation;
                     31:
                     32:   -- DESCRIPTION :
                     33:   --   returns p1 `after' p2
                     34:   --   (1 3 -2) * (2 -1 3) = (3 -1 -2)
                     35:   -- REQUIRED :
                     36:   --   p1'range = p2'range
                     37:
                     38:   function inv ( p : Permutation ) return Permutation;
                     39:
                     40:   -- DESCRIPTION :
                     41:   --   inv(p)*p = p*inv(p) = the identical transformation
                     42:
                     43: end Permutations;