# slaexc.f(3) [centos man page]

slaexc.f(3) LAPACK slaexc.f(3)NAME

slaexc.f-SYNOPSIS

Functions/Subroutines subroutine slaexc (WANTQ, N, T, LDT, Q, LDQ, J1, N1, N2, WORK, INFO) SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation.Function/Subroutine Documentation subroutine slaexc (logicalWANTQ, integerN, real, dimension( ldt, * )T, integerLDT, real, dimension( ldq, * )Q, integerLDQ, integerJ1, integerN1, integerN2, real, dimension( * )WORK, integerINFO) SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation. Purpose: SLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in an upper quasi-triangular matrix T by an orthogonal similarity transformation. T must be in Schur canonical form, that is, block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each 2-by-2 diagonal block has its diagonal elemnts equal and its off-diagonal elements of opposite sign. Parameters: WANTQ WANTQ is LOGICAL = .TRUE. : accumulate the transformation in the matrix Q; = .FALSE.: do not accumulate the transformation. N N is INTEGER The order of the matrix T. N >= 0. T T is REAL array, dimension (LDT,N) On entry, the upper quasi-triangular matrix T, in Schur canonical form. On exit, the updated matrix T, again in Schur canonical form. LDT LDT is INTEGER The leading dimension of the array T. LDT >= max(1,N). Q Q is REAL array, dimension (LDQ,N) On entry, if WANTQ is .TRUE., the orthogonal matrix Q. On exit, if WANTQ is .TRUE., the updated matrix Q. If WANTQ is .FALSE., Q is not referenced. LDQ LDQ is INTEGER The leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N. J1 J1 is INTEGER The index of the first row of the first block T11. N1 N1 is INTEGER The order of the first block T11. N1 = 0, 1 or 2. N2 N2 is INTEGER The order of the second block T22. N2 = 0, 1 or 2. WORK WORK is REAL array, dimension (N) INFO INFO is INTEGER = 0: successful exit = 1: the transformed matrix T would be too far from Schur form; the blocks are not swapped and T and Q are unchanged. Author: Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd. Date: September 2012 Definition at line 138 of file slaexc.f.AuthorGenerated automatically by Doxygen for LAPACK from the source code.Version 3.4.2Tue Sep 25 2012 slaexc.f(3)

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DLAEXC(l)) DLAEXC(l)NAME

DLAEXC - swap adjacent diagonal blocks T11 and T22 of order 1 or 2 in an upper quasi-triangular matrix T by an orthogonal similarity trans- formationSYNOPSIS

SUBROUTINE DLAEXC( WANTQ, N, T, LDT, Q, LDQ, J1, N1, N2, WORK, INFO ) LOGICAL WANTQ INTEGER INFO, J1, LDQ, LDT, N, N1, N2 DOUBLE PRECISION Q( LDQ, * ), T( LDT, * ), WORK( * )PURPOSE

DLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in an upper quasi-triangular matrix T by an orthogonal similarity trans- formation. T must be in Schur canonical form, that is, block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each 2-by-2 diagonal block has its diagonal elemnts equal and its off-diagonal elements of opposite sign.ARGUMENTS

WANTQ (input) LOGICAL = .TRUE. : accumulate the transformation in the matrix Q; = .FALSE.: do not accumulate the transformation. 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 canonical form. On exit, the updated matrix T, 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 WANTQ is .TRUE., the orthogonal matrix Q. On exit, if WANTQ is .TRUE., the updated matrix Q. If WANTQ is .FALSE., Q is not referenced. LDQ (input) INTEGER The leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N. J1 (input) INTEGER The index of the first row of the first block T11. N1 (input) INTEGER The order of the first block T11. N1 = 0, 1 or 2. N2 (input) INTEGER The order of the second block T22. N2 = 0, 1 or 2. WORK (workspace) DOUBLE PRECISION array, dimension (N) INFO (output) INTEGER = 0: successful exit = 1: the transformed matrix T would be too far from Schur form; the blocks are not swapped and T and Q are unchanged.LAPACK version 3.015 June 2000 DLAEXC(l)