zlags2.f(3)

NAME
zlags2.f -

SYNOPSIS

  Functions/Subroutines

subroutine zlags2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)
ZLAGS2

Function/Subroutine Documentation

  subroutine zlags2 (logicalUPPER, double precisionA1, complex*16A2, double precisionA3, double precisionB1, complex*16B2, double precisionB3, double precisionCSU, complex*16SNU, double precisionCSV, complex*16SNV, double precisionCSQ, complex*16SNQ)

ZLAGS2

Purpose:

     ZLAGS2 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:
    UPPER

              UPPER is LOGICAL
              = .TRUE.: the input matrices A and B are upper triangular.
              = .FALSE.: the input matrices A and B are lower triangular.

    A1

              A1 is DOUBLE PRECISION

    A2

              A2 is COMPLEX*16

    A3

              A3 is DOUBLE PRECISION
              On entry, A1, A2 and A3 are elements of the input 2-by-2
              upper (lower) triangular matrix A.

    B1

              B1 is DOUBLE PRECISION

    B2

              B2 is COMPLEX*16

    B3

              B3 is DOUBLE PRECISION
              On entry, B1, B2 and B3 are elements of the input 2-by-2
              upper (lower) triangular matrix B.

    CSU

              CSU is DOUBLE PRECISION

    SNU

              SNU is COMPLEX*16
              The desired unitary matrix U.

    CSV

              CSV is DOUBLE PRECISION

    SNV

              SNV is COMPLEX*16
              The desired unitary matrix V.

    CSQ

              CSQ is DOUBLE PRECISION

    SNQ

              SNQ is COMPLEX*16
              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 zlags2.f.

Author

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