Reordered Schur Factorization
DESCRIPTION:
Reorders the Schur factorization of a square matrix.
USAGE: 
schurmod(x, indexes=<see below>, vectors=<see below>)
REQUIRED ARGUMENTS:
x:
an object of class schur.Matrix.
OPTIONAL ARGUMENTS:
indexes:
a integer vector of length 2 indicating which indexes of the eigenvalues involved in the reordering. If indexes = c(i,j), then the block or element in row i is moved to row j by a sequence of transpositions between adjacents blocks or elements.
vectors:
a logical value telling whether or not to update and return the Schur vectors if they are present in x. The default is to update and return the Schur vectors.
VALUE:
An object of class schur.Matrix containing the reordered Schur form and (optionally) the corresponding Schur vectors.
DETAILS:
Based on the functions dtrexc and ztrexc from Lapack (Anderson et al. 1994).
REFERENCES:
Anderson, E., et al. (1994). LAPACK User's Guide, 2nd edition, SIAM, Philadelphia.
SEE ALSO:
schur.Matrix , schur.Matrix.object
BUGS:
Does not return the proper ordering in all cases. A bug report will be filed with the Lapack developers.
EXAMPLES: 
n <- 9
x <- Matrix( rnorm( n*n, sd = 100), nrow = n, ncol = n)
schur.x <- schur(x)                                 # schur factorization
schur.x <- schurmod(schur.x, indexes = c(1,n))      # reordered factorization