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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 More...
 

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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