SUBROUTINE STRSYL( TRANA, TRANB, ISGN, M, N, A, LDA, B, LDB, C,
$ LDC, SCALE, INFO )
CHARACTER TRANA, TRANB
INTEGER INFO, ISGN, LDA, LDB, LDC, M, N
REAL SCALE
REAL A( LDA, * ), B( LDB, * ), C( LDC, * )
REAL ZERO, ONE
PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
LOGICAL NOTRNA, NOTRNB
INTEGER IERR, J, K, K1, K2, KNEXT, L, L1, L2, LNEXT
REAL A11, BIGNUM, DA11, DB, EPS, SCALOC, SGN, SMIN,
$ SMLNUM, SUML, SUMR, XNORM
REAL DUM( 1 ), VEC( 2, 2 ), X( 2, 2 )
LOGICAL LSAME
REAL SDOT, SLAMCH, SLANGE
EXTERNAL LSAME, SDOT, SLAMCH, SLANGE
EXTERNAL SLABAD, SLALN2, SLASY2, SSCAL, XERBLA
INTRINSIC ABS, MAX, MIN, REAL
NOTRNA = LSAME( TRANA, 'N' )
NOTRNB = LSAME( TRANB, 'N' )
INFO = 0
IF( .NOT.NOTRNA .AND. .NOT.LSAME( TRANA, 'T' ) .AND. .NOT.
$ LSAME( TRANA, 'C' ) ) THEN
INFO = -1
ELSE IF( .NOT.NOTRNB .AND. .NOT.LSAME( TRANB, 'T' ) .AND. .NOT.
$ LSAME( TRANB, 'C' ) ) THEN
INFO = -2
ELSE IF( ISGN.NE.1 .AND. ISGN.NE.-1 ) THEN
INFO = -3
ELSE IF( M.LT.0 ) THEN
INFO = -4
ELSE IF( N.LT.0 ) THEN
INFO = -5
ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
INFO = -7
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -9
ELSE IF( LDC.LT.MAX( 1, M ) ) THEN
INFO = -11
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'STRSYL', -INFO )
RETURN
END IF
IF( M.EQ.0 .OR. N.EQ.0 )
$ RETURN
EPS = SLAMCH( 'P' )
SMLNUM = SLAMCH( 'S' )
BIGNUM = ONE / SMLNUM
CALL SLABAD( SMLNUM, BIGNUM )
SMLNUM = SMLNUM*REAL( M*N ) / EPS
BIGNUM = ONE / SMLNUM
SMIN = MAX( SMLNUM, EPS*SLANGE( 'M', M, M, A, LDA, DUM ),
$ EPS*SLANGE( 'M', N, N, B, LDB, DUM ) )
SCALE = ONE
SGN = ISGN
IF( NOTRNA .AND. NOTRNB ) THEN
LNEXT = 1
DO 70 L = 1, N
IF( L.LT.LNEXT )
$ GO TO 70
IF( L.EQ.N ) THEN
L1 = L
L2 = L
ELSE
IF( B( L+1, L ).NE.ZERO ) THEN
L1 = L
L2 = L + 1
LNEXT = L + 2
ELSE
L1 = L
L2 = L
LNEXT = L + 1
END IF
END IF
KNEXT = M
DO 60 K = M, 1, -1
IF( K.GT.KNEXT )
$ GO TO 60
IF( K.EQ.1 ) THEN
K1 = K
K2 = K
ELSE
IF( A( K, K-1 ).NE.ZERO ) THEN
K1 = K - 1
K2 = K
KNEXT = K - 2
ELSE
K1 = K
K2 = K
KNEXT = K - 1
END IF
END IF
IF( L1.EQ.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( M-K1, A( K1, MIN( K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SCALOC = ONE
A11 = A( K1, K1 ) + SGN*B( L1, L1 )
DA11 = ABS( A11 )
IF( DA11.LE.SMIN ) THEN
A11 = SMIN
DA11 = SMIN
INFO = 1
END IF
DB = ABS( VEC( 1, 1 ) )
IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN
IF( DB.GT.BIGNUM*DA11 )
$ SCALOC = ONE / DB
END IF
X( 1, 1 ) = ( VEC( 1, 1 )*SCALOC ) / A11
IF( SCALOC.NE.ONE ) THEN
DO 10 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
10 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
ELSE IF( L1.EQ.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
CALL SLALN2( .FALSE., 2, 1, SMIN, ONE, A( K1, K1 ),
$ LDA, ONE, ONE, VEC, 2, -SGN*B( L1, L1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 20 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
20 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K2, L1 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( M-K1, A( K1, MIN( K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = SGN*( C( K1, L1 )-( SUML+SGN*SUMR ) )
SUML = SDOT( M-K1, A( K1, MIN( K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L2 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 2, 1 ) = SGN*( C( K1, L2 )-( SUML+SGN*SUMR ) )
CALL SLALN2( .TRUE., 2, 1, SMIN, ONE, B( L1, L1 ),
$ LDB, ONE, ONE, VEC, 2, -SGN*A( K1, K1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 40 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
40 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L2 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 1, 2 ) = C( K1, L2 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L2 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 2, 2 ) = C( K2, L2 ) - ( SUML+SGN*SUMR )
CALL SLASY2( .FALSE., .FALSE., ISGN, 2, 2,
$ A( K1, K1 ), LDA, B( L1, L1 ), LDB, VEC,
$ 2, SCALOC, X, 2, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 50 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
50 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 1, 2 )
C( K2, L1 ) = X( 2, 1 )
C( K2, L2 ) = X( 2, 2 )
END IF
60 CONTINUE
70 CONTINUE
ELSE IF( .NOT.NOTRNA .AND. NOTRNB ) THEN
LNEXT = 1
DO 130 L = 1, N
IF( L.LT.LNEXT )
$ GO TO 130
IF( L.EQ.N ) THEN
L1 = L
L2 = L
ELSE
IF( B( L+1, L ).NE.ZERO ) THEN
L1 = L
L2 = L + 1
LNEXT = L + 2
ELSE
L1 = L
L2 = L
LNEXT = L + 1
END IF
END IF
KNEXT = 1
DO 120 K = 1, M
IF( K.LT.KNEXT )
$ GO TO 120
IF( K.EQ.M ) THEN
K1 = K
K2 = K
ELSE
IF( A( K+1, K ).NE.ZERO ) THEN
K1 = K
K2 = K + 1
KNEXT = K + 2
ELSE
K1 = K
K2 = K
KNEXT = K + 1
END IF
END IF
IF( L1.EQ.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SCALOC = ONE
A11 = A( K1, K1 ) + SGN*B( L1, L1 )
DA11 = ABS( A11 )
IF( DA11.LE.SMIN ) THEN
A11 = SMIN
DA11 = SMIN
INFO = 1
END IF
DB = ABS( VEC( 1, 1 ) )
IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN
IF( DB.GT.BIGNUM*DA11 )
$ SCALOC = ONE / DB
END IF
X( 1, 1 ) = ( VEC( 1, 1 )*SCALOC ) / A11
IF( SCALOC.NE.ONE ) THEN
DO 80 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
80 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
ELSE IF( L1.EQ.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
CALL SLALN2( .TRUE., 2, 1, SMIN, ONE, A( K1, K1 ),
$ LDA, ONE, ONE, VEC, 2, -SGN*B( L1, L1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 90 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
90 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K2, L1 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = SGN*( C( K1, L1 )-( SUML+SGN*SUMR ) )
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 2, 1 ) = SGN*( C( K1, L2 )-( SUML+SGN*SUMR ) )
CALL SLALN2( .TRUE., 2, 1, SMIN, ONE, B( L1, L1 ),
$ LDB, ONE, ONE, VEC, 2, -SGN*A( K1, K1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 100 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
100 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( L1-1, C( K1, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 1, 2 ) = C( K1, L2 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L1 ), 1 )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( L1-1, C( K2, 1 ), LDC, B( 1, L2 ), 1 )
VEC( 2, 2 ) = C( K2, L2 ) - ( SUML+SGN*SUMR )
CALL SLASY2( .TRUE., .FALSE., ISGN, 2, 2, A( K1, K1 ),
$ LDA, B( L1, L1 ), LDB, VEC, 2, SCALOC, X,
$ 2, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 110 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
110 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 1, 2 )
C( K2, L1 ) = X( 2, 1 )
C( K2, L2 ) = X( 2, 2 )
END IF
120 CONTINUE
130 CONTINUE
ELSE IF( .NOT.NOTRNA .AND. .NOT.NOTRNB ) THEN
LNEXT = N
DO 190 L = N, 1, -1
IF( L.GT.LNEXT )
$ GO TO 190
IF( L.EQ.1 ) THEN
L1 = L
L2 = L
ELSE
IF( B( L, L-1 ).NE.ZERO ) THEN
L1 = L - 1
L2 = L
LNEXT = L - 2
ELSE
L1 = L
L2 = L
LNEXT = L - 1
END IF
END IF
KNEXT = 1
DO 180 K = 1, M
IF( K.LT.KNEXT )
$ GO TO 180
IF( K.EQ.M ) THEN
K1 = K
K2 = K
ELSE
IF( A( K+1, K ).NE.ZERO ) THEN
K1 = K
K2 = K + 1
KNEXT = K + 2
ELSE
K1 = K
K2 = K
KNEXT = K + 1
END IF
END IF
IF( L1.EQ.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L1, C( K1, MIN( L1+1, N ) ), LDC,
$ B( L1, MIN( L1+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SCALOC = ONE
A11 = A( K1, K1 ) + SGN*B( L1, L1 )
DA11 = ABS( A11 )
IF( DA11.LE.SMIN ) THEN
A11 = SMIN
DA11 = SMIN
INFO = 1
END IF
DB = ABS( VEC( 1, 1 ) )
IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN
IF( DB.GT.BIGNUM*DA11 )
$ SCALOC = ONE / DB
END IF
X( 1, 1 ) = ( VEC( 1, 1 )*SCALOC ) / A11
IF( SCALOC.NE.ONE ) THEN
DO 140 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
140 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
ELSE IF( L1.EQ.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
CALL SLALN2( .TRUE., 2, 1, SMIN, ONE, A( K1, K1 ),
$ LDA, ONE, ONE, VEC, 2, -SGN*B( L1, L1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 150 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
150 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K2, L1 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = SGN*( C( K1, L1 )-( SUML+SGN*SUMR ) )
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = SGN*( C( K1, L2 )-( SUML+SGN*SUMR ) )
CALL SLALN2( .FALSE., 2, 1, SMIN, ONE, B( L1, L1 ),
$ LDB, ONE, ONE, VEC, 2, -SGN*A( K1, K1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 160 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
160 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K1 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN( L2+1, N ) ), LDB )
VEC( 1, 2 ) = C( K1, L2 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L1 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( K1-1, A( 1, K2 ), 1, C( 1, L2 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN(L2+1, N ) ), LDB )
VEC( 2, 2 ) = C( K2, L2 ) - ( SUML+SGN*SUMR )
CALL SLASY2( .TRUE., .TRUE., ISGN, 2, 2, A( K1, K1 ),
$ LDA, B( L1, L1 ), LDB, VEC, 2, SCALOC, X,
$ 2, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 170 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
170 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 1, 2 )
C( K2, L1 ) = X( 2, 1 )
C( K2, L2 ) = X( 2, 2 )
END IF
180 CONTINUE
190 CONTINUE
ELSE IF( NOTRNA .AND. .NOT.NOTRNB ) THEN
LNEXT = N
DO 250 L = N, 1, -1
IF( L.GT.LNEXT )
$ GO TO 250
IF( L.EQ.1 ) THEN
L1 = L
L2 = L
ELSE
IF( B( L, L-1 ).NE.ZERO ) THEN
L1 = L - 1
L2 = L
LNEXT = L - 2
ELSE
L1 = L
L2 = L
LNEXT = L - 1
END IF
END IF
KNEXT = M
DO 240 K = M, 1, -1
IF( K.GT.KNEXT )
$ GO TO 240
IF( K.EQ.1 ) THEN
K1 = K
K2 = K
ELSE
IF( A( K, K-1 ).NE.ZERO ) THEN
K1 = K - 1
K2 = K
KNEXT = K - 2
ELSE
K1 = K
K2 = K
KNEXT = K - 1
END IF
END IF
IF( L1.EQ.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( M-K1, A( K1, MIN(K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L1 ), 1 )
SUMR = SDOT( N-L1, C( K1, MIN( L1+1, N ) ), LDC,
$ B( L1, MIN( L1+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SCALOC = ONE
A11 = A( K1, K1 ) + SGN*B( L1, L1 )
DA11 = ABS( A11 )
IF( DA11.LE.SMIN ) THEN
A11 = SMIN
DA11 = SMIN
INFO = 1
END IF
DB = ABS( VEC( 1, 1 ) )
IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN
IF( DB.GT.BIGNUM*DA11 )
$ SCALOC = ONE / DB
END IF
X( 1, 1 ) = ( VEC( 1, 1 )*SCALOC ) / A11
IF( SCALOC.NE.ONE ) THEN
DO 200 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
200 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
ELSE IF( L1.EQ.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
CALL SLALN2( .FALSE., 2, 1, SMIN, ONE, A( K1, K1 ),
$ LDA, ONE, ONE, VEC, 2, -SGN*B( L1, L1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 210 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
210 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K2, L1 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.EQ.K2 ) THEN
SUML = SDOT( M-K1, A( K1, MIN( K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = SGN*( C( K1, L1 )-( SUML+SGN*SUMR ) )
SUML = SDOT( M-K1, A( K1, MIN( K1+1, M ) ), LDA,
$ C( MIN( K1+1, M ), L2 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = SGN*( C( K1, L2 )-( SUML+SGN*SUMR ) )
CALL SLALN2( .FALSE., 2, 1, SMIN, ONE, B( L1, L1 ),
$ LDB, ONE, ONE, VEC, 2, -SGN*A( K1, K1 ),
$ ZERO, X, 2, SCALOC, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 220 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
220 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 2, 1 )
ELSE IF( L1.NE.L2 .AND. K1.NE.K2 ) THEN
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 1, 1 ) = C( K1, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K1, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L2 ), 1 )
SUMR = SDOT( N-L2, C( K1, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN( L2+1, N ) ), LDB )
VEC( 1, 2 ) = C( K1, L2 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L1 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L1, MIN( L2+1, N ) ), LDB )
VEC( 2, 1 ) = C( K2, L1 ) - ( SUML+SGN*SUMR )
SUML = SDOT( M-K2, A( K2, MIN( K2+1, M ) ), LDA,
$ C( MIN( K2+1, M ), L2 ), 1 )
SUMR = SDOT( N-L2, C( K2, MIN( L2+1, N ) ), LDC,
$ B( L2, MIN( L2+1, N ) ), LDB )
VEC( 2, 2 ) = C( K2, L2 ) - ( SUML+SGN*SUMR )
CALL SLASY2( .FALSE., .TRUE., ISGN, 2, 2, A( K1, K1 ),
$ LDA, B( L1, L1 ), LDB, VEC, 2, SCALOC, X,
$ 2, XNORM, IERR )
IF( IERR.NE.0 )
$ INFO = 1
IF( SCALOC.NE.ONE ) THEN
DO 230 J = 1, N
CALL SSCAL( M, SCALOC, C( 1, J ), 1 )
230 CONTINUE
SCALE = SCALE*SCALOC
END IF
C( K1, L1 ) = X( 1, 1 )
C( K1, L2 ) = X( 1, 2 )
C( K2, L1 ) = X( 2, 1 )
C( K2, L2 ) = X( 2, 2 )
END IF
240 CONTINUE
250 CONTINUE
END IF
RETURN
END