1DLASY2(1)           LAPACK auxiliary routine (version 3.1)           DLASY2(1)
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NAME

6       DLASY2  -  for  the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in   op(TL)*X +
7       ISGN*X*op(TR) = SCALE*B,
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SYNOPSIS

10       SUBROUTINE DLASY2( 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           DOUBLE         PRECISION SCALE, XNORM
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19           DOUBLE         PRECISION B( LDB, * ), TL( LDTL, * ), TR( LDTR, * ),
20                          X( LDX, * )
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PURPOSE

23       DLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in
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25       where TL is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN  =  1  or
26       -1.  op(T) = T or T', where T' denotes the transpose of T.
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ARGUMENTS

30       LTRANL  (input) LOGICAL
31               On  entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL,
32               = .TRUE., op(TL) = TL'.
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34       LTRANR  (input) LOGICAL
35               On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) =  TR,
36               = .TRUE., op(TR) = TR'.
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38       ISGN    (input) INTEGER
39               On  entry, ISGN specifies the sign of the equation as described
40               before. ISGN may only be 1 or -1.
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42       N1      (input) INTEGER
43               On entry, N1 specifies the order of matrix TL.  N1 may only  be
44               0, 1 or 2.
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46       N2      (input) INTEGER
47               On  entry, N2 specifies the order of matrix TR.  N2 may only be
48               0, 1 or 2.
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50       TL      (input) DOUBLE PRECISION array, dimension (LDTL,2)
51               On entry, TL contains an N1 by N1 matrix.
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53       LDTL    (input) INTEGER
54               The leading dimension of the matrix TL. LDTL >= max(1,N1).
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56       TR      (input) DOUBLE PRECISION array, dimension (LDTR,2)
57               On entry, TR contains an N2 by N2 matrix.
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59       LDTR    (input) INTEGER
60               The leading dimension of the matrix TR. LDTR >= max(1,N2).
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62       B       (input) DOUBLE PRECISION array, dimension (LDB,2)
63               On entry, the N1 by N2 matrix B contains the right-hand side of
64               the equation.
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66       LDB     (input) INTEGER
67               The leading dimension of the matrix B. LDB >= max(1,N1).
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69       SCALE   (output) DOUBLE PRECISION
70               On  exit, SCALE contains the scale factor. SCALE is chosen less
71               than or equal to 1 to prevent the solution overflowing.
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73       X       (output) DOUBLE PRECISION array, dimension (LDX,2)
74               On exit, X contains the N1 by N2 solution.
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76       LDX     (input) INTEGER
77               The leading dimension of the matrix X. LDX >= max(1,N1).
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79       XNORM   (output) DOUBLE PRECISION
80               On exit, XNORM is the infinity-norm of the solution.
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82       INFO    (output) INTEGER
83               On exit, INFO is set to 0: successful exit.
84               1: TL and TR have too close eigenvalues, so TL or  TR  is  per‐
85               turbed  to  get a nonsingular equation.  NOTE: In the interests
86               of speed, this routine does not check the inputs for errors.
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90 LAPACK auxiliary routine (versionNo3v.e1m)ber 2006                       DLASY2(1)