SUBROUTINE CHEGS2( ITYPE, UPLO, N, A, LDA, B, LDB, INFO )
CHARACTER UPLO
INTEGER INFO, ITYPE, LDA, LDB, N
COMPLEX A( LDA, * ), B( LDB, * )
REAL ONE, HALF
PARAMETER ( ONE = 1.0E+0, HALF = 0.5E+0 )
COMPLEX CONE
PARAMETER ( CONE = ( 1.0E+0, 0.0E+0 ) )
LOGICAL UPPER
INTEGER K
REAL AKK, BKK
COMPLEX CT
EXTERNAL CAXPY, CHER2, CLACGV, CSSCAL, CTRMV, CTRSV,
$ XERBLA
INTRINSIC MAX
LOGICAL LSAME
EXTERNAL LSAME
INFO = 0
UPPER = LSAME( UPLO, 'U' )
IF( ITYPE.LT.1 .OR. ITYPE.GT.3 ) THEN
INFO = -1
ELSE IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -3
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -5
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -7
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CHEGS2', -INFO )
RETURN
END IF
IF( ITYPE.EQ.1 ) THEN
IF( UPPER ) THEN
DO 10 K = 1, N
AKK = A( K, K )
BKK = B( K, K )
AKK = AKK / BKK**2
A( K, K ) = AKK
IF( K.LT.N ) THEN
CALL CSSCAL( N-K, ONE / BKK, A( K, K+1 ), LDA )
CT = -HALF*AKK
CALL CLACGV( N-K, A( K, K+1 ), LDA )
CALL CLACGV( N-K, B( K, K+1 ), LDB )
CALL CAXPY( N-K, CT, B( K, K+1 ), LDB, A( K, K+1 ),
$ LDA )
CALL CHER2( UPLO, N-K, -CONE, A( K, K+1 ), LDA,
$ B( K, K+1 ), LDB, A( K+1, K+1 ), LDA )
CALL CAXPY( N-K, CT, B( K, K+1 ), LDB, A( K, K+1 ),
$ LDA )
CALL CLACGV( N-K, B( K, K+1 ), LDB )
CALL CTRSV( UPLO, 'Conjugate transpose', 'Non-unit',
$ N-K, B( K+1, K+1 ), LDB, A( K, K+1 ),
$ LDA )
CALL CLACGV( N-K, A( K, K+1 ), LDA )
END IF
10 CONTINUE
ELSE
DO 20 K = 1, N
AKK = A( K, K )
BKK = B( K, K )
AKK = AKK / BKK**2
A( K, K ) = AKK
IF( K.LT.N ) THEN
CALL CSSCAL( N-K, ONE / BKK, A( K+1, K ), 1 )
CT = -HALF*AKK
CALL CAXPY( N-K, CT, B( K+1, K ), 1, A( K+1, K ), 1 )
CALL CHER2( UPLO, N-K, -CONE, A( K+1, K ), 1,
$ B( K+1, K ), 1, A( K+1, K+1 ), LDA )
CALL CAXPY( N-K, CT, B( K+1, K ), 1, A( K+1, K ), 1 )
CALL CTRSV( UPLO, 'No transpose', 'Non-unit', N-K,
$ B( K+1, K+1 ), LDB, A( K+1, K ), 1 )
END IF
20 CONTINUE
END IF
ELSE
IF( UPPER ) THEN
DO 30 K = 1, N
AKK = A( K, K )
BKK = B( K, K )
CALL CTRMV( UPLO, 'No transpose', 'Non-unit', K-1, B,
$ LDB, A( 1, K ), 1 )
CT = HALF*AKK
CALL CAXPY( K-1, CT, B( 1, K ), 1, A( 1, K ), 1 )
CALL CHER2( UPLO, K-1, CONE, A( 1, K ), 1, B( 1, K ), 1,
$ A, LDA )
CALL CAXPY( K-1, CT, B( 1, K ), 1, A( 1, K ), 1 )
CALL CSSCAL( K-1, BKK, A( 1, K ), 1 )
A( K, K ) = AKK*BKK**2
30 CONTINUE
ELSE
DO 40 K = 1, N
AKK = A( K, K )
BKK = B( K, K )
CALL CLACGV( K-1, A( K, 1 ), LDA )
CALL CTRMV( UPLO, 'Conjugate transpose', 'Non-unit', K-1,
$ B, LDB, A( K, 1 ), LDA )
CT = HALF*AKK
CALL CLACGV( K-1, B( K, 1 ), LDB )
CALL CAXPY( K-1, CT, B( K, 1 ), LDB, A( K, 1 ), LDA )
CALL CHER2( UPLO, K-1, CONE, A( K, 1 ), LDA, B( K, 1 ),
$ LDB, A, LDA )
CALL CAXPY( K-1, CT, B( K, 1 ), LDB, A( K, 1 ), LDA )
CALL CLACGV( K-1, B( K, 1 ), LDB )
CALL CSSCAL( K-1, BKK, A( K, 1 ), LDA )
CALL CLACGV( K-1, A( K, 1 ), LDA )
A( K, K ) = AKK*BKK**2
40 CONTINUE
END IF
END IF
RETURN
END