SUBROUTINE CTBSV (UPLO, TRANS, DIAG, N, K, A, LDA, X, INCX)
C .. Scalar Arguments ..
INTEGER INCX, K, LDA, N
CHARACTER*1 DIAG, TRANS, UPLO
C .. Array Arguments ..
COMPLEX A( LDA, * ), X( * )
C .. Parameters ..
COMPLEX ZERO
PARAMETER ( ZERO = ( 0.0E+0, 0.0E+0 ) )
C .. Local Scalars ..
COMPLEX TEMP
INTEGER I, INFO, IX, J, JX, KPLUS1, KX, L
LOGICAL NOCONJ, NOUNIT
C .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
C .. External Subroutines ..
EXTERNAL XERBLA
C .. Intrinsic Functions ..
INTRINSIC CONJG, MAX, MIN
C***FIRST EXECUTABLE STATEMENT CTBSV
C
C Test the input parameters.
C
INFO = 0
IF ( .NOT.LSAME( UPLO , 'U' ).AND.
$ .NOT.LSAME( UPLO , 'L' ) )THEN
INFO = 1
ELSE IF( .NOT.LSAME( TRANS, 'N' ).AND.
$ .NOT.LSAME( TRANS, 'T' ).AND.
$ .NOT.LSAME( TRANS, 'C' ) )THEN
INFO = 2
ELSE IF( .NOT.LSAME( DIAG , 'U' ).AND.
$ .NOT.LSAME( DIAG , 'N' ) )THEN
INFO = 3
ELSE IF( N.LT.0 )THEN
INFO = 4
ELSE IF( K.LT.0 )THEN
INFO = 5
ELSE IF( LDA.LT.( K + 1 ) )THEN
INFO = 7
ELSE IF( INCX.EQ.0 )THEN
INFO = 9
END IF
IF( INFO.NE.0 )THEN
CALL XERBLA( 'CTBSV ', INFO )
RETURN
END IF
C
C Quick return if possible.
C
IF( N.EQ.0 )
$ RETURN
C
NOCONJ = LSAME( TRANS, 'T' )
NOUNIT = LSAME( DIAG , 'N' )
C
C Set up the start point in X if the increment is not unity. This
C will be ( N - 1 )*INCX too small for descending loops.
C
IF( INCX.LE.0 )THEN
KX = 1 - ( N - 1 )*INCX
ELSE IF( INCX.NE.1 )THEN
KX = 1
END IF
C
C Start the operations. In this version the elements of A are
C accessed by sequentially with one pass through A.
C
IF( LSAME( TRANS, 'N' ) )THEN
C
C Form x := inv( A )*x.
C
IF( LSAME( UPLO, 'U' ) )THEN
KPLUS1 = K + 1
IF( INCX.EQ.1 )THEN
DO 20, J = N, 1, -1
IF( X( J ).NE.ZERO )THEN
L = KPLUS1 - J
IF( NOUNIT )
$ X( J ) = X( J )/A( KPLUS1, J )
TEMP = X( J )
DO 10, I = J - 1, MAX( 1, J - K ), -1
X( I ) = X( I ) - TEMP*A( L + I, J )
10 CONTINUE
END IF
20 CONTINUE
ELSE
KX = KX + ( N - 1 )*INCX
JX = KX
DO 40, J = N, 1, -1
KX = KX - INCX
IF( X( JX ).NE.ZERO )THEN
IX = KX
L = KPLUS1 - J
IF( NOUNIT )
$ X( JX ) = X( JX )/A( KPLUS1, J )
TEMP = X( JX )
DO 30, I = J - 1, MAX( 1, J - K ), -1
X( IX ) = X( IX ) - TEMP*A( L + I, J )
IX = IX - INCX
30 CONTINUE
END IF
JX = JX - INCX
40 CONTINUE
END IF
ELSE
IF( INCX.EQ.1 )THEN
DO 60, J = 1, N
IF( X( J ).NE.ZERO )THEN
L = 1 - J
IF( NOUNIT )
$ X( J ) = X( J )/A( 1, J )
TEMP = X( J )
DO 50, I = J + 1, MIN( N, J + K )
X( I ) = X( I ) - TEMP*A( L + I, J )
50 CONTINUE
END IF
60 CONTINUE
ELSE
JX = KX
DO 80, J = 1, N
KX = KX + INCX
IF( X( JX ).NE.ZERO )THEN
IX = KX
L = 1 - J
IF( NOUNIT )
$ X( JX ) = X( JX )/A( 1, J )
TEMP = X( JX )
DO 70, I = J + 1, MIN( N, J + K )
X( IX ) = X( IX ) - TEMP*A( L + I, J )
IX = IX + INCX
70 CONTINUE
END IF
JX = JX + INCX
80 CONTINUE
END IF
END IF
ELSE
C
C Form x := inv( A' )*x or x := inv( conjg( A') )*x.
C
IF( LSAME( UPLO, 'U' ) )THEN
KPLUS1 = K + 1
IF( INCX.EQ.1 )THEN
DO 110, J = 1, N
TEMP = X( J )
L = KPLUS1 - J
IF( NOCONJ )THEN
DO 90, I = MAX( 1, J - K ), J - 1
TEMP = TEMP - A( L + I, J )*X( I )
90 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/A( KPLUS1, J )
ELSE
DO 100, I = MAX( 1, J - K ), J - 1
TEMP = TEMP - CONJG( A( L + I, J ) )*X( I )
100 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/CONJG( A( KPLUS1, J ) )
END IF
X( J ) = TEMP
110 CONTINUE
ELSE
JX = KX
DO 140, J = 1, N
TEMP = X( JX )
IX = KX
L = KPLUS1 - J
IF( NOCONJ )THEN
DO 120, I = MAX( 1, J - K ), J - 1
TEMP = TEMP - A( L + I, J )*X( IX )
IX = IX + INCX
120 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/A( KPLUS1, J )
ELSE
DO 130, I = MAX( 1, J - K ), J - 1
TEMP = TEMP - CONJG( A( L + I, J ) )*X( IX )
IX = IX + INCX
130 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/CONJG( A( KPLUS1, J ) )
END IF
X( JX ) = TEMP
JX = JX + INCX
IF( J.GT.K )
$ KX = KX + INCX
140 CONTINUE
END IF
ELSE
IF( INCX.EQ.1 )THEN
DO 170, J = N, 1, -1
TEMP = X( J )
L = 1 - J
IF( NOCONJ )THEN
DO 150, I = MIN( N, J + K ), J + 1, -1
TEMP = TEMP - A( L + I, J )*X( I )
150 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/A( 1, J )
ELSE
DO 160, I = MIN( N, J + K ), J + 1, -1
TEMP = TEMP - CONJG( A( L + I, J ) )*X( I )
160 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/CONJG( A( 1, J ) )
END IF
X( J ) = TEMP
170 CONTINUE
ELSE
KX = KX + ( N - 1 )*INCX
JX = KX
DO 200, J = N, 1, -1
TEMP = X( JX )
IX = KX
L = 1 - J
IF( NOCONJ )THEN
DO 180, I = MIN( N, J + K ), J + 1, -1
TEMP = TEMP - A( L + I, J )*X( IX )
IX = IX - INCX
180 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/A( 1, J )
ELSE
DO 190, I = MIN( N, J + K ), J + 1, -1
TEMP = TEMP - CONJG( A( L + I, J ) )*X( IX )
IX = IX - INCX
190 CONTINUE
IF( NOUNIT )
$ TEMP = TEMP/CONJG( A( 1, J ) )
END IF
X( JX ) = TEMP
JX = JX - INCX
IF( ( N - J ).GE.K )
$ KX = KX - INCX
200 CONTINUE
END IF
END IF
END IF
C
RETURN
C
C End of CTBSV .
C
END