SUBROUTINE CHPTRS( UPLO, N, NRHS, AP, IPIV, B, LDB, INFO )
CHARACTER UPLO
INTEGER INFO, LDB, N, NRHS
INTEGER IPIV( * )
COMPLEX AP( * ), B( LDB, * )
COMPLEX ONE
PARAMETER ( ONE = ( 1.0E+0, 0.0E+0 ) )
LOGICAL UPPER
INTEGER J, K, KC, KP
REAL S
COMPLEX AK, AKM1, AKM1K, BK, BKM1, DENOM
LOGICAL LSAME
EXTERNAL LSAME
EXTERNAL CGEMV, CGERU, CLACGV, CSSCAL, CSWAP, XERBLA
INTRINSIC CONJG, MAX, REAL
INFO = 0
UPPER = LSAME( UPLO, 'U' )
IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( NRHS.LT.0 ) THEN
INFO = -3
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -7
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CHPTRS', -INFO )
RETURN
END IF
IF( N.EQ.0 .OR. NRHS.EQ.0 )
$ RETURN
IF( UPPER ) THEN
K = N
KC = N*( N+1 ) / 2 + 1
10 CONTINUE
IF( K.LT.1 )
$ GO TO 30
KC = KC - K
IF( IPIV( K ).GT.0 ) THEN
KP = IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
CALL CGERU( K-1, NRHS, -ONE, AP( KC ), 1, B( K, 1 ), LDB,
$ B( 1, 1 ), LDB )
S = REAL( ONE ) / REAL( AP( KC+K-1 ) )
CALL CSSCAL( NRHS, S, B( K, 1 ), LDB )
K = K - 1
ELSE
KP = -IPIV( K )
IF( KP.NE.K-1 )
$ CALL CSWAP( NRHS, B( K-1, 1 ), LDB, B( KP, 1 ), LDB )
CALL CGERU( K-2, NRHS, -ONE, AP( KC ), 1, B( K, 1 ), LDB,
$ B( 1, 1 ), LDB )
CALL CGERU( K-2, NRHS, -ONE, AP( KC-( K-1 ) ), 1,
$ B( K-1, 1 ), LDB, B( 1, 1 ), LDB )
AKM1K = AP( KC+K-2 )
AKM1 = AP( KC-1 ) / AKM1K
AK = AP( KC+K-1 ) / CONJG( AKM1K )
DENOM = AKM1*AK - ONE
DO 20 J = 1, NRHS
BKM1 = B( K-1, J ) / AKM1K
BK = B( K, J ) / CONJG( AKM1K )
B( K-1, J ) = ( AK*BKM1-BK ) / DENOM
B( K, J ) = ( AKM1*BK-BKM1 ) / DENOM
20 CONTINUE
KC = KC - K + 1
K = K - 2
END IF
GO TO 10
30 CONTINUE
K = 1
KC = 1
40 CONTINUE
IF( K.GT.N )
$ GO TO 50
IF( IPIV( K ).GT.0 ) THEN
IF( K.GT.1 ) THEN
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', K-1, NRHS, -ONE, B,
$ LDB, AP( KC ), 1, ONE, B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K, 1 ), LDB )
END IF
KP = IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
KC = KC + K
K = K + 1
ELSE
IF( K.GT.1 ) THEN
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', K-1, NRHS, -ONE, B,
$ LDB, AP( KC ), 1, ONE, B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K+1, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', K-1, NRHS, -ONE, B,
$ LDB, AP( KC+K ), 1, ONE, B( K+1, 1 ), LDB )
CALL CLACGV( NRHS, B( K+1, 1 ), LDB )
END IF
KP = -IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
KC = KC + 2*K + 1
K = K + 2
END IF
GO TO 40
50 CONTINUE
ELSE
K = 1
KC = 1
60 CONTINUE
IF( K.GT.N )
$ GO TO 80
IF( IPIV( K ).GT.0 ) THEN
KP = IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
IF( K.LT.N )
$ CALL CGERU( N-K, NRHS, -ONE, AP( KC+1 ), 1, B( K, 1 ),
$ LDB, B( K+1, 1 ), LDB )
S = REAL( ONE ) / REAL( AP( KC ) )
CALL CSSCAL( NRHS, S, B( K, 1 ), LDB )
KC = KC + N - K + 1
K = K + 1
ELSE
KP = -IPIV( K )
IF( KP.NE.K+1 )
$ CALL CSWAP( NRHS, B( K+1, 1 ), LDB, B( KP, 1 ), LDB )
IF( K.LT.N-1 ) THEN
CALL CGERU( N-K-1, NRHS, -ONE, AP( KC+2 ), 1, B( K, 1 ),
$ LDB, B( K+2, 1 ), LDB )
CALL CGERU( N-K-1, NRHS, -ONE, AP( KC+N-K+2 ), 1,
$ B( K+1, 1 ), LDB, B( K+2, 1 ), LDB )
END IF
AKM1K = AP( KC+1 )
AKM1 = AP( KC ) / CONJG( AKM1K )
AK = AP( KC+N-K+1 ) / AKM1K
DENOM = AKM1*AK - ONE
DO 70 J = 1, NRHS
BKM1 = B( K, J ) / CONJG( AKM1K )
BK = B( K+1, J ) / AKM1K
B( K, J ) = ( AK*BKM1-BK ) / DENOM
B( K+1, J ) = ( AKM1*BK-BKM1 ) / DENOM
70 CONTINUE
KC = KC + 2*( N-K ) + 1
K = K + 2
END IF
GO TO 60
80 CONTINUE
K = N
KC = N*( N+1 ) / 2 + 1
90 CONTINUE
IF( K.LT.1 )
$ GO TO 100
KC = KC - ( N-K+1 )
IF( IPIV( K ).GT.0 ) THEN
IF( K.LT.N ) THEN
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', N-K, NRHS, -ONE,
$ B( K+1, 1 ), LDB, AP( KC+1 ), 1, ONE,
$ B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K, 1 ), LDB )
END IF
KP = IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
K = K - 1
ELSE
IF( K.LT.N ) THEN
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', N-K, NRHS, -ONE,
$ B( K+1, 1 ), LDB, AP( KC+1 ), 1, ONE,
$ B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K, 1 ), LDB )
CALL CLACGV( NRHS, B( K-1, 1 ), LDB )
CALL CGEMV( 'Conjugate transpose', N-K, NRHS, -ONE,
$ B( K+1, 1 ), LDB, AP( KC-( N-K ) ), 1, ONE,
$ B( K-1, 1 ), LDB )
CALL CLACGV( NRHS, B( K-1, 1 ), LDB )
END IF
KP = -IPIV( K )
IF( KP.NE.K )
$ CALL CSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
KC = KC - ( N-K+2 )
K = K - 2
END IF
GO TO 90
100 CONTINUE
END IF
RETURN
END