#include "blaswrap.h"
#include "f2c.h"
/* Subroutine */ int strexc_(char *compq, integer *n, real *t, integer *ldt,
real *q, integer *ldq, integer *ifst, integer *ilst, real *work,
integer *info)
{
/* -- LAPACK routine (version 3.0) --
Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
Courant Institute, Argonne National Lab, and Rice University
March 31, 1993
Purpose
=======
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.
Arguments
=========
COMPQ (input) CHARACTER*1
= 'V': update the matrix Q of Schur vectors;
= 'N': do not update Q.
N (input) INTEGER
The order of the matrix T. N >= 0.
T (input/output) 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.
LDT (input) INTEGER
The leading dimension of the array T. LDT >= max(1,N).
Q (input/output) 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.
LDQ (input) INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
IFST (input/output) INTEGER
ILST (input/output) 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.
WORK (workspace) REAL array, dimension (N)
INFO (output) 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.
=====================================================================
Decode and test the input arguments.
Parameter adjustments */
/* Table of constant values */
static integer c__1 = 1;
static integer c__2 = 2;
/* System generated locals */
integer q_dim1, q_offset, t_dim1, t_offset, i__1;
/* Local variables */
static integer here;
extern logical lsame_(char *, char *);
static logical wantq;
extern /* Subroutine */ int xerbla_(char *, integer *), slaexc_(
logical *, integer *, real *, integer *, real *, integer *,
integer *, integer *, integer *, real *, integer *);
static integer nbnext, nbf, nbl;
#define t_ref(a_1,a_2) t[(a_2)*t_dim1 + a_1]
t_dim1 = *ldt;
t_offset = 1 + t_dim1 * 1;
t -= t_offset;
q_dim1 = *ldq;
q_offset = 1 + q_dim1 * 1;
q -= q_offset;
--work;
/* Function Body */
*info = 0;
wantq = lsame_(compq, "V");
if (! wantq && ! lsame_(compq, "N")) {
*info = -1;
} else if (*n < 0) {
*info = -2;
} else if (*ldt < max(1,*n)) {
*info = -4;
} else if (*ldq < 1 || wantq && *ldq < max(1,*n)) {
*info = -6;
} else if (*ifst < 1 || *ifst > *n) {
*info = -7;
} else if (*ilst < 1 || *ilst > *n) {
*info = -8;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("STREXC", &i__1);
return 0;
}
/* Quick return if possible */
if (*n <= 1) {
return 0;
}
/* Determine the first row of specified block
and find out it is 1 by 1 or 2 by 2. */
if (*ifst > 1) {
if (t_ref(*ifst, *ifst - 1) != 0.f) {
--(*ifst);
}
}
nbf = 1;
if (*ifst < *n) {
if (t_ref(*ifst + 1, *ifst) != 0.f) {
nbf = 2;
}
}
/* Determine the first row of the final block
and find out it is 1 by 1 or 2 by 2. */
if (*ilst > 1) {
if (t_ref(*ilst, *ilst - 1) != 0.f) {
--(*ilst);
}
}
nbl = 1;
if (*ilst < *n) {
if (t_ref(*ilst + 1, *ilst) != 0.f) {
nbl = 2;
}
}
if (*ifst == *ilst) {
return 0;
}
if (*ifst < *ilst) {
/* Update ILST */
if (nbf == 2 && nbl == 1) {
--(*ilst);
}
if (nbf == 1 && nbl == 2) {
++(*ilst);
}
here = *ifst;
L10:
/* Swap block with next one below */
if (nbf == 1 || nbf == 2) {
/* Current block either 1 by 1 or 2 by 2 */
nbnext = 1;
if (here + nbf + 1 <= *n) {
if (t_ref(here + nbf + 1, here + nbf) != 0.f) {
nbnext = 2;
}
}
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &here, &
nbf, &nbnext, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
here += nbnext;
/* Test if 2 by 2 block breaks into two 1 by 1 blocks */
if (nbf == 2) {
if (t_ref(here + 1, here) == 0.f) {
nbf = 3;
}
}
} else {
/* Current block consists of two 1 by 1 blocks each of which
must be swapped individually */
nbnext = 1;
if (here + 3 <= *n) {
if (t_ref(here + 3, here + 2) != 0.f) {
nbnext = 2;
}
}
i__1 = here + 1;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &i__1, &
c__1, &nbnext, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
if (nbnext == 1) {
/* Swap two 1 by 1 blocks, no problems possible */
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
here, &c__1, &nbnext, &work[1], info);
++here;
} else {
/* Recompute NBNEXT in case 2 by 2 split */
if (t_ref(here + 2, here + 1) == 0.f) {
nbnext = 1;
}
if (nbnext == 2) {
/* 2 by 2 Block did not split */
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
here, &c__1, &nbnext, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
here += 2;
} else {
/* 2 by 2 Block did split */
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
here, &c__1, &c__1, &work[1], info);
i__1 = here + 1;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
i__1, &c__1, &c__1, &work[1], info);
here += 2;
}
}
}
if (here < *ilst) {
goto L10;
}
} else {
here = *ifst;
L20:
/* Swap block with next one above */
if (nbf == 1 || nbf == 2) {
/* Current block either 1 by 1 or 2 by 2 */
nbnext = 1;
if (here >= 3) {
if (t_ref(here - 1, here - 2) != 0.f) {
nbnext = 2;
}
}
i__1 = here - nbnext;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &i__1, &
nbnext, &nbf, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
here -= nbnext;
/* Test if 2 by 2 block breaks into two 1 by 1 blocks */
if (nbf == 2) {
if (t_ref(here + 1, here) == 0.f) {
nbf = 3;
}
}
} else {
/* Current block consists of two 1 by 1 blocks each of which
must be swapped individually */
nbnext = 1;
if (here >= 3) {
if (t_ref(here - 1, here - 2) != 0.f) {
nbnext = 2;
}
}
i__1 = here - nbnext;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &i__1, &
nbnext, &c__1, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
if (nbnext == 1) {
/* Swap two 1 by 1 blocks, no problems possible */
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
here, &nbnext, &c__1, &work[1], info);
--here;
} else {
/* Recompute NBNEXT in case 2 by 2 split */
if (t_ref(here, here - 1) == 0.f) {
nbnext = 1;
}
if (nbnext == 2) {
/* 2 by 2 Block did not split */
i__1 = here - 1;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
i__1, &c__2, &c__1, &work[1], info);
if (*info != 0) {
*ilst = here;
return 0;
}
here += -2;
} else {
/* 2 by 2 Block did split */
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
here, &c__1, &c__1, &work[1], info);
i__1 = here - 1;
slaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, &
i__1, &c__1, &c__1, &work[1], info);
here += -2;
}
}
}
if (here > *ilst) {
goto L20;
}
}
*ilst = here;
return 0;
/* End of STREXC */
} /* strexc_ */
#undef t_ref