1SLAGS2(1) LAPACK auxiliary routine (version 3.2) SLAGS2(1)
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6 SLAGS2 - computes 2-by-2 orthogonal matrices U, V and Q, such that if (
7 UPPER ) then U'*A*Q = U'*( A1 A2 )*Q = ( x 0 ) ( 0 A3 ) ( x x ) and
8 V'*B*Q = V'*( B1 B2 )*Q = ( x 0 ) ( 0 B3 ) ( x x ) or if ( .NOT.UPPER
9 ) then U'*A*Q = U'*( A1 0 )*Q = ( x x ) ( A2 A3 ) ( 0 x ) and
10 V'*B*Q = V'*( B1 0 )*Q = ( x x ) ( B2 B3 ) ( 0 x ) The rows of the
11 transformed A and B are parallel, where U = ( CSU SNU ), V = ( CSV
12 SNV ), Q = ( CSQ SNQ ) ( -SNU CSU ) ( -SNV CSV ) ( -SNQ CSQ ) Z'
13 denotes the transpose of Z
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16 SUBROUTINE SLAGS2( UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV,
17 CSQ, SNQ )
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19 LOGICAL UPPER
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21 REAL A1, A2, A3, B1, B2, B3, CSQ, CSU, CSV, SNQ, SNU, SNV
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24 SLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such that if (
25 UPPER ) then
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28 UPPER (input) LOGICAL
29 = .TRUE.: the input matrices A and B are upper triangular.
30 = .FALSE.: the input matrices A and B are lower triangular.
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32 A1 (input) REAL
33 A2 (input) REAL A3 (input) REAL On entry, A1, A2 and
34 A3 are elements of the input 2-by-2 upper (lower) triangular
35 matrix A.
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37 B1 (input) REAL
38 B2 (input) REAL B3 (input) REAL On entry, B1, B2 and
39 B3 are elements of the input 2-by-2 upper (lower) triangular
40 matrix B.
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42 CSU (output) REAL
43 SNU (output) REAL The desired orthogonal matrix U.
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45 CSV (output) REAL
46 SNV (output) REAL The desired orthogonal matrix V.
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48 CSQ (output) REAL
49 SNQ (output) REAL The desired orthogonal matrix Q.
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53 LAPACK auxiliary routine (versionNo3v.e2m)ber 2008 SLAGS2(1)