slags2.f (3)

Functions/Subroutines

subroutine slags2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)

SLAGS2 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.

subroutine slags2 (logicalUPPER, realA1, realA2, realA3, realB1, realB2, realB3, realCSU, realSNU, realCSV, realSNV, realCSQ, realSNQ)

SLAGS2 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:

 SLAGS2 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 REAL

A2

          A2 is REAL

A3

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

B1

          B1 is REAL

B2

          B2 is REAL

B3

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

CSU

          CSU is REAL

SNU

          SNU is REAL
          The desired orthogonal matrix U.

CSV

          CSV is REAL

SNV

          SNV is REAL
          The desired orthogonal matrix V.

CSQ

          CSQ is REAL

SNQ

          SNQ is REAL
          The desired orthogonal matrix Q.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 152 of file slags2.f.

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