#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int dtrexc_(char *compq, integer *n, doublereal *t, integer * ldt, doublereal *q, integer *ldq, integer *ifst, integer *ilst, doublereal *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 ======= DTREXC 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 DHSEQR), 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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 dlaexc_(logical *, integer *, doublereal *, integer *, doublereal *, integer *, integer *, integer *, integer *, doublereal *, integer *), xerbla_(char *, 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_("DTREXC", &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.) { --(*ifst); } } nbf = 1; if (*ifst < *n) { if (t_ref(*ifst + 1, *ifst) != 0.) { 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.) { --(*ilst); } } nbl = 1; if (*ilst < *n) { if (t_ref(*ilst + 1, *ilst) != 0.) { 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.) { nbnext = 2; } } dlaexc_(&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.) { 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.) { nbnext = 2; } } i__1 = here + 1; dlaexc_(&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 */ dlaexc_(&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.) { nbnext = 1; } if (nbnext == 2) { /* 2 by 2 Block did not split */ dlaexc_(&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 */ dlaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, & here, &c__1, &c__1, &work[1], info); i__1 = here + 1; dlaexc_(&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.) { nbnext = 2; } } i__1 = here - nbnext; dlaexc_(&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.) { 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.) { nbnext = 2; } } i__1 = here - nbnext; dlaexc_(&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 */ dlaexc_(&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.) { nbnext = 1; } if (nbnext == 2) { /* 2 by 2 Block did not split */ i__1 = here - 1; dlaexc_(&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 */ dlaexc_(&wantq, n, &t[t_offset], ldt, &q[q_offset], ldq, & here, &c__1, &c__1, &work[1], info); i__1 = here - 1; dlaexc_(&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 DTREXC */ } /* dtrexc_ */ #undef t_ref