LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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clags2.f File Reference

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Functions/Subroutines

subroutine clags2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)
 CLAGS2

Function/Subroutine Documentation

subroutine clags2 ( logical  UPPER,
real  A1,
complex  A2,
real  A3,
real  B1,
complex  B2,
real  B3,
real  CSU,
complex  SNU,
real  CSV,
complex  SNV,
real  CSQ,
complex  SNQ 
)

CLAGS2

Download CLAGS2 + dependencies [TGZ] [ZIP] [TXT]
Purpose: 
 CLAGS2 computes 2-by-2 unitary matrices U, V and Q, such
 that if ( UPPER ) then

           U**H *A*Q = U**H *( A1 A2 )*Q = ( x  0  )
                             ( 0  A3 )     ( x  x  )
 and
           V**H*B*Q = V**H *( B1 B2 )*Q = ( x  0  )
                            ( 0  B3 )     ( x  x  )

 or if ( .NOT.UPPER ) then

           U**H *A*Q = U**H *( A1 0  )*Q = ( x  x  )
                             ( A2 A3 )     ( 0  x  )
 and
           V**H *B*Q = V**H *( B1 0  )*Q = ( x  x  )
                             ( B2 B3 )     ( 0  x  )
 where

   U = (   CSU    SNU ), V = (  CSV    SNV ),
       ( -SNU**H  CSU )      ( -SNV**H CSV )

   Q = (   CSQ    SNQ )
       ( -SNQ**H  CSQ )

 The rows of the transformed A and B are parallel. Moreover, if the
 input 2-by-2 matrix A is not zero, then the transformed (1,1) entry
 of A is not zero. If the input matrices A and B are both not zero,
 then the transformed (2,2) element of B is not zero, except when the
 first rows of input A and B are parallel and the second rows are
 zero.
Parameters:
[in]UPPER
          UPPER is LOGICAL
          = .TRUE.: the input matrices A and B are upper triangular.
          = .FALSE.: the input matrices A and B are lower triangular.
[in]A1
          A1 is REAL
[in]A2
          A2 is COMPLEX
[in]A3
          A3 is REAL
          On entry, A1, A2 and A3 are elements of the input 2-by-2
          upper (lower) triangular matrix A.
[in]B1
          B1 is REAL
[in]B2
          B2 is COMPLEX
[in]B3
          B3 is REAL
          On entry, B1, B2 and B3 are elements of the input 2-by-2
          upper (lower) triangular matrix B.
[out]CSU
          CSU is REAL
[out]SNU
          SNU is COMPLEX
          The desired unitary matrix U.
[out]CSV
          CSV is REAL
[out]SNV
          SNV is COMPLEX
          The desired unitary matrix V.
[out]CSQ
          CSQ is REAL
[out]SNQ
          SNQ is COMPLEX
          The desired unitary matrix Q.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011

Definition at line 158 of file clags2.f.

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