1SLASY2(1) LAPACK auxiliary routine (version 3.2) SLASY2(1)
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6 SLASY2 - solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in
7 op(TL)*X + ISGN*X*op(TR) = SCALE*B,
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10 SUBROUTINE SLASY2( LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B,
11 LDB, SCALE, X, LDX, XNORM, INFO )
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13 LOGICAL LTRANL, LTRANR
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15 INTEGER INFO, ISGN, LDB, LDTL, LDTR, LDX, N1, N2
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17 REAL SCALE, XNORM
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19 REAL B( LDB, * ), TL( LDTL, * ), TR( LDTR, * ), X( LDX, *
20 )
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23 SLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in where TL
24 is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN = 1 or -1. op(T)
25 = T or T', where T' denotes the transpose of T.
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28 LTRANL (input) LOGICAL
29 On entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL,
30 = .TRUE., op(TL) = TL'.
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32 LTRANR (input) LOGICAL
33 On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) = TR,
34 = .TRUE., op(TR) = TR'.
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36 ISGN (input) INTEGER
37 On entry, ISGN specifies the sign of the equation as described
38 before. ISGN may only be 1 or -1.
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40 N1 (input) INTEGER
41 On entry, N1 specifies the order of matrix TL. N1 may only be
42 0, 1 or 2.
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44 N2 (input) INTEGER
45 On entry, N2 specifies the order of matrix TR. N2 may only be
46 0, 1 or 2.
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48 TL (input) REAL array, dimension (LDTL,2)
49 On entry, TL contains an N1 by N1 matrix.
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51 LDTL (input) INTEGER
52 The leading dimension of the matrix TL. LDTL >= max(1,N1).
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54 TR (input) REAL array, dimension (LDTR,2)
55 On entry, TR contains an N2 by N2 matrix.
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57 LDTR (input) INTEGER
58 The leading dimension of the matrix TR. LDTR >= max(1,N2).
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60 B (input) REAL array, dimension (LDB,2)
61 On entry, the N1 by N2 matrix B contains the right-hand side of
62 the equation.
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64 LDB (input) INTEGER
65 The leading dimension of the matrix B. LDB >= max(1,N1).
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67 SCALE (output) REAL
68 On exit, SCALE contains the scale factor. SCALE is chosen less
69 than or equal to 1 to prevent the solution overflowing.
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71 X (output) REAL array, dimension (LDX,2)
72 On exit, X contains the N1 by N2 solution.
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74 LDX (input) INTEGER
75 The leading dimension of the matrix X. LDX >= max(1,N1).
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77 XNORM (output) REAL
78 On exit, XNORM is the infinity-norm of the solution.
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80 INFO (output) INTEGER
81 On exit, INFO is set to 0: successful exit.
82 1: TL and TR have too close eigenvalues, so TL or TR is per‐
83 turbed to get a nonsingular equation. NOTE: In the interests
84 of speed, this routine does not check the inputs for errors.
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88 LAPACK auxiliary routine (versionNo3v.e2m)ber 2008 SLASY2(1)