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---
:name: ztrexc
:md5sum: 22440e97c892aee6b265e87024968d43
:category: :subroutine
:arguments:
- compq:
:type: char
:intent: input
- n:
:type: integer
:intent: input
- t:
:type: doublecomplex
:intent: input/output
:dims:
- ldt
- n
- ldt:
:type: integer
:intent: input
- q:
:type: doublecomplex
:intent: input/output
:dims:
- ldq
- n
- ldq:
:type: integer
:intent: input
- ifst:
:type: integer
:intent: input
- ilst:
:type: integer
:intent: input
- info:
:type: integer
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* ZTREXC reorders the Schur factorization of a complex matrix\n\
* A = Q*T*Q**H, so that the diagonal element of T with row index IFST\n\
* is moved to row ILST.\n\
*\n\
* The Schur form T is reordered by a unitary similarity transformation\n\
* Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by\n\
* postmultplying it with Z.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* COMPQ (input) CHARACTER*1\n\
* = 'V': update the matrix Q of Schur vectors;\n\
* = 'N': do not update Q.\n\
*\n\
* N (input) INTEGER\n\
* The order of the matrix T. N >= 0.\n\
*\n\
* T (input/output) COMPLEX*16 array, dimension (LDT,N)\n\
* On entry, the upper triangular matrix T.\n\
* On exit, the reordered upper triangular matrix.\n\
*\n\
* LDT (input) INTEGER\n\
* The leading dimension of the array T. LDT >= max(1,N).\n\
*\n\
* Q (input/output) COMPLEX*16 array, dimension (LDQ,N)\n\
* On entry, if COMPQ = 'V', the matrix Q of Schur vectors.\n\
* On exit, if COMPQ = 'V', Q has been postmultiplied by the\n\
* unitary transformation matrix Z which reorders T.\n\
* If COMPQ = 'N', Q is not referenced.\n\
*\n\
* LDQ (input) INTEGER\n\
* The leading dimension of the array Q. LDQ >= max(1,N).\n\
*\n\
* IFST (input) INTEGER\n\
* ILST (input) INTEGER\n\
* Specify the reordering of the diagonal elements of T:\n\
* The element with row index IFST is moved to row ILST by a\n\
* sequence of transpositions between adjacent elements.\n\
* 1 <= IFST <= N; 1 <= ILST <= N.\n\
*\n\
* INFO (output) INTEGER\n\
* = 0: successful exit\n\
* < 0: if INFO = -i, the i-th argument had an illegal value\n\
*\n\n\
* =====================================================================\n\
*\n\
* .. Local Scalars ..\n LOGICAL WANTQ\n INTEGER K, M1, M2, M3\n DOUBLE PRECISION CS\n COMPLEX*16 SN, T11, T22, TEMP\n\
* ..\n\
* .. External Functions ..\n LOGICAL LSAME\n EXTERNAL LSAME\n\
* ..\n\
* .. External Subroutines ..\n EXTERNAL XERBLA, ZLARTG, ZROT\n\
* ..\n\
* .. Intrinsic Functions ..\n INTRINSIC DCONJG, MAX\n\
* ..\n"
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