dgebak dgebal dgehrd dhsein dhseqr dorghr dormhr dtrevc3 dtrexc dtrsen dtrsna dtrsyl

dtrexc() void dtrexc ( char  compq, int  n, int  ldt, double  t[], int  ldq, double  q[], int *  ifst, int *  ilst, double  work[], int *  info  ) Reordering of real Schur factorization of real matrix Purpose This routine 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 x 1 and 2 x 2 diagonal blocks; each 2 x 2 diagonal block has its diagonal elements equal and its off-diagonal elements of opposite sign. Parameters [in] compq = 'V': Update the matrix Q of Schur vectors. = 'N': Do not update Q. [in] n Order of the matrix T. (n >= 0) (If n = 0, returns without computation) [in] ldt Leading dimension of the two dimensional array t[][]. (ldt >= max(1, n)) [in,out] t[][] Array t[lt][ldt] (lt >= n) [in] The upper quasi-triangular matrix T, in Schur canonical form. [out] The reordered upper quasi-triangular matrix, again in Schur canonical form. [in] ldq Leading dimension of the two dimensional array q[][]. (ldq >= 1 if compq = 'N', ldq >= max(1, n) if compq = 'V') [in,out] q[][] Array q[lq][ldq] (lq >= n) If compq = 'V', [in] The matrix Q of Schur vectors. [out] Q has been postmultiplied by the orthogonal transformation matrix Z which reorders T. If compq = 'N', q[][] is not referenced. [in,out] ifst [in,out] ilst [in] 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. [out] If ifst pointed on entry to the second row of a 2 x 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) [out] work[] Array work[lwork] (lwork >= n) Work array. [out] info = 0: Successful exit = -1: The argument compq had an illegal value (copq != 'V' nor 'N') = -2: The argument n had an illegal value (n < 0) = -3: The argument ldt had an illegal value (ldt < max(1, n)) = -5: The argument ldq had an illegal value (ldq too small) = -7: The argument ifst had an illegal value (ifst < 1 or ifst > n) = -8: The argument ilst had an illegal value (ilst < 1 or ilst > n) = 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. Reference LAPACK