SRC/dlags2.f(3)

NAME
SRC/dlags2.f

SYNOPSIS

  Functions/Subroutines
subroutine dlags2 (upper, a1, a2, a3, b1, b2, b3, csu, snu, csv, snv, csq, snq)
DLAGS2 computes 2-by-2 orthogonal matrices U, V, and Q, and applies them to matrices A and B such that the rows of the transformed A and B are parallel.

Function/Subroutine Documentation

  subroutine dlags2 (logical upper, double precision a1, double precision a2, double precision a3, double precision b1, double precision b2, double precision b3, double precision csu, double precision snu, double precision csv, double precision snv, double precision csq, double precision snq)

DLAGS2 computes 2-by-2 orthogonal matrices U, V, and Q, and applies them to matrices A and B such that the rows of the transformed A and B are parallel.

Purpose:

     DLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such
     that if ( UPPER ) then
               U**T *A*Q = U**T *( A1 A2 )*Q = ( x  0  )
                                 ( 0  A3 )     ( x  x  )
     and
               V**T*B*Q = V**T *( B1 B2 )*Q = ( x  0  )
                                ( 0  B3 )     ( x  x  )
     or if ( .NOT.UPPER ) then
               U**T *A*Q = U**T *( A1 0  )*Q = ( x  x  )
                                 ( A2 A3 )     ( 0  x  )
     and
               V**T*B*Q = V**T*( B1 0  )*Q = ( x  x  )
                               ( B2 B3 )     ( 0  x  )
     The rows of the transformed A and B are parallel, where
       U = (  CSU  SNU ), V = (  CSV SNV ), Q = (  CSQ   SNQ )
           ( -SNU  CSU )      ( -SNV CSV )      ( -SNQ   CSQ )
     Z**T denotes the transpose of Z.

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 DOUBLE PRECISION

    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 DOUBLE PRECISION

    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 DOUBLE PRECISION
              The desired orthogonal matrix U.

    CSV

              CSV is DOUBLE PRECISION

    SNV

              SNV is DOUBLE PRECISION
              The desired orthogonal matrix V.

    CSQ

              CSQ is DOUBLE PRECISION

    SNQ

              SNQ is DOUBLE PRECISION
              The desired orthogonal matrix Q.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 150 of file dlags2.f.

Author

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