.TH "SRC/strexc.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*-
.ad l
.nh
.SH NAME
SRC/strexc.f
.SH SYNOPSIS
.br
.PP
.SS "Functions/Subroutines"

.in +1c
.ti -1c
.RI "subroutine \fBstrexc\fP (compq, n, t, ldt, q, ldq, ifst, ilst, work, info)"
.br
.RI "\fBSTREXC\fP "
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine strexc (character compq, integer n, real, dimension( ldt, * ) t, integer ldt, real, dimension( ldq, * ) q, integer ldq, integer ifst, integer ilst, real, dimension( * ) work, integer info)"

.PP
\fBSTREXC\fP  
.PP
\fBPurpose:\fP
.RS 4

.PP
.nf
 STREXC reorders the real Schur factorization of a real matrix
 A = Q*T*Q**T, so that the diagonal block of T with row index IFST is
 moved to row ILST\&.

 The real Schur form T is reordered by an orthogonal similarity
 transformation Z**T*T*Z, and optionally the matrix Q of Schur vectors
 is updated by postmultiplying it with Z\&.

 T must be in Schur canonical form (as returned by SHSEQR), that is,
 block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each
 2-by-2 diagonal block has its diagonal elements equal and its
 off-diagonal elements of opposite sign\&.
.fi
.PP
 
.RE
.PP
\fBParameters\fP
.RS 4
\fICOMPQ\fP 
.PP
.nf
          COMPQ is CHARACTER*1
          = 'V':  update the matrix Q of Schur vectors;
          = 'N':  do not update Q\&.
.fi
.PP
.br
\fIN\fP 
.PP
.nf
          N is INTEGER
          The order of the matrix T\&. N >= 0\&.
          If N == 0 arguments ILST and IFST may be any value\&.
.fi
.PP
.br
\fIT\fP 
.PP
.nf
          T is REAL array, dimension (LDT,N)
          On entry, the upper quasi-triangular matrix T, in Schur
          Schur canonical form\&.
          On exit, the reordered upper quasi-triangular matrix, again
          in Schur canonical form\&.
.fi
.PP
.br
\fILDT\fP 
.PP
.nf
          LDT is INTEGER
          The leading dimension of the array T\&. LDT >= max(1,N)\&.
.fi
.PP
.br
\fIQ\fP 
.PP
.nf
          Q is REAL 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
          orthogonal transformation matrix Z which reorders T\&.
          If COMPQ = 'N', Q is not referenced\&.
.fi
.PP
.br
\fILDQ\fP 
.PP
.nf
          LDQ is INTEGER
          The leading dimension of the array Q\&.  LDQ >= 1, and if
          COMPQ = 'V', LDQ >= max(1,N)\&.
.fi
.PP
.br
\fIIFST\fP 
.PP
.nf
          IFST is INTEGER
.fi
.PP
.br
\fIILST\fP 
.PP
.nf
          ILST is INTEGER

          Specify the reordering of the diagonal blocks of T\&.
          The block with row index IFST is moved to row ILST, by a
          sequence of transpositions between adjacent blocks\&.
          On exit, if IFST pointed on entry to the second row of a
          2-by-2 block, it is changed to point to the first row; ILST
          always points to the first row of the block in its final
          position (which may differ from its input value by +1 or -1)\&.
          1 <= IFST <= N; 1 <= ILST <= N\&.
.fi
.PP
.br
\fIWORK\fP 
.PP
.nf
          WORK is REAL array, dimension (N)
.fi
.PP
.br
\fIINFO\fP 
.PP
.nf
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          = 1:  two adjacent blocks were too close to swap (the problem
                is very ill-conditioned); T may have been partially
                reordered, and ILST points to the first row of the
                current position of the block being moved\&.
.fi
.PP
 
.RE
.PP
\fBAuthor\fP
.RS 4
Univ\&. of Tennessee 
.PP
Univ\&. of California Berkeley 
.PP
Univ\&. of Colorado Denver 
.PP
NAG Ltd\&. 
.RE
.PP

.PP
Definition at line \fB146\fP of file \fBstrexc\&.f\fP\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for LAPACK from the source code\&.