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DTREXCRun Method

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.

Namespace: DotNumerics.LinearAlgebra.CSLapack
Assembly: DWSIM.MathOps.DotNumerics (in DWSIM.MathOps.DotNumerics.dll) Version: 1.0.0.0 (1.0.0.0)
Syntax
Copy
public void Run(
	string COMPQ,
	int N,
	ref double[] T,
	int offset_t,
	int LDT,
	ref double[] Q,
	int offset_q,
	int LDQ,
	ref int IFST,
	ref int ILST,
	ref double[] WORK,
	int offset_work,
	ref int INFO
)
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Parameters

COMPQ  String
(input) CHARACTER*1 = 'V': update the matrix Q of Schur vectors; = 'N': do not update Q.
N  Int32
(input) INTEGER The order of the matrix T. N .GE. 0.
T  Double
must be in Schur canonical form (as returned by DHSEQR), that is,
offset_t  Int32
 
LDT  Int32
(input) INTEGER The leading dimension of the array T. LDT .GE. max(1,N).
Q  Double
(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.
offset_q  Int32
 
LDQ  Int32
(input) INTEGER The leading dimension of the array Q. LDQ .GE. max(1,N).
IFST  Int32
(input/output) INTEGER
ILST  Int32
(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 .LE. IFST .LE. N; 1 .LE. ILST .LE. N.
WORK  Double
(workspace) DOUBLE PRECISION array, dimension (N)
offset_work  Int32
 
INFO  Int32
(output) INTEGER = 0: successful exit .LT. 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.
See Also