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  4. ZLAGS2(3)

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zlags2.f(3) LAPACK 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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