ZTREXC reorders the Schur factorization of a complex matrix


 A = Q*T*Q**H, so that the diagonal element of T with row index IFST


 is moved to row ILST.


 The Schur form T is reordered by a unitary similarity transformation


 Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by


 postmultplying it with Z.

COMPQ

          COMPQ is CHARACTER*1


          = 'V':  update the matrix Q of Schur vectors;


          = 'N':  do not update Q.

N

          N is INTEGER


          The order of the matrix T. N >= 0.


          If N == 0 arguments ILST and IFST may be any value.

T

          T is COMPLEX*16 array, dimension (LDT,N)


          On entry, the upper triangular matrix T.


          On exit, the reordered upper triangular matrix.

LDT

          LDT is INTEGER


          The leading dimension of the array T. LDT >= max(1,N).

Q

          Q is COMPLEX*16 array, dimension (LDQ,N)


          On entry, if COMPQ = 'V', the matrix Q of Schur vectors.


          On exit, if COMPQ = 'V', Q has been postmultiplied by the


          unitary transformation matrix Z which reorders T.


          If COMPQ = 'N', Q is not referenced.

LDQ

          LDQ is INTEGER


          The leading dimension of the array Q.  LDQ >= 1, and if


          COMPQ = 'V', LDQ >= max(1,N).

IFST

          IFST is INTEGER

ILST

          ILST is INTEGER


          Specify the reordering of the diagonal elements of T:


          The element with row index IFST is moved to row ILST by a


          sequence of transpositions between adjacent elements.


          1 <= IFST <= N; 1 <= ILST <= N.

INFO

          INFO is INTEGER


          = 0:  successful exit


          < 0:  if INFO = -i, the i-th argument had an illegal value

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016