dlags2-f(3)

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 (logicalUPPER, double precisionA1, double precisionA2, double precisionA3, double precisionB1, double precisionB2, double precisionB3, double precisionCSU, double precisionSNU, double precisionCSV, double precisionSNV, double precisionCSQ, double precisionSNQ)

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 is DOUBLE PRECISION

 A2 is DOUBLE PRECISION

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

 B1 is DOUBLE PRECISION

 B2 is DOUBLE PRECISION

 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.

Date:

September 2012

Definition at line 152 of file dlags2.f.

Author

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