template<int SizeAtCompileTime, int MaxSizeAtCompileTime, typename _StorageIndex>
class Eigen::Transpositions< SizeAtCompileTime, MaxSizeAtCompileTime, _StorageIndex >

Represents a sequence of transpositions (row/column interchange)

Template Parameters

SizeAtCompileTime	the number of transpositions, or Dynamic
MaxSizeAtCompileTime	the maximum number of transpositions, or Dynamic. This optional parameter defaults to SizeAtCompileTime. Most of the time, you should not have to specify it.

This class represents a permutation transformation as a sequence of n transpositions \([T_{n-1} \ldots T_{i} \ldots T_{0}]\). It is internally stored as a vector of integers indices. Each transposition \( T_{i} \) applied on the left of a matrix ( \( T_{i} M\)) interchanges the rows i and indices[i] of the matrix M. A transposition applied on the right (e.g., \( M T_{i}\)) yields a column interchange.

Compared to the class PermutationMatrix, such a sequence of transpositions is what is computed during a decomposition with pivoting, and it is faster when applying the permutation in-place.

To apply a sequence of transpositions to a matrix, simply use the operator * as in the following example:

Transpositions tr;
MatrixXf mat;
mat = tr * mat;

In this example, we detect that the matrix appears on both side, and so the transpositions are applied in-place without any temporary or extra copy.

See also

class PermutationMatrix