SUBROUTINE ZHEGST( ITYPE, UPLO, N, A, LDA, B, LDB, INFO )
CHARACTER UPLO
INTEGER INFO, ITYPE, LDA, LDB, N
COMPLEX*16 A( LDA, * ), B( LDB, * )
DOUBLE PRECISION ONE
PARAMETER ( ONE = 1.0D+0 )
COMPLEX*16 CONE, HALF
PARAMETER ( CONE = ( 1.0D+0, 0.0D+0 ),
$ HALF = ( 0.5D+0, 0.0D+0 ) )
LOGICAL UPPER
INTEGER K, KB, NB
EXTERNAL XERBLA, ZHEGS2, ZHEMM, ZHER2K, ZTRMM, ZTRSM
INTRINSIC MAX, MIN
LOGICAL LSAME
INTEGER ILAENV
EXTERNAL LSAME, ILAENV
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( 'ZHEGST', -INFO )
RETURN
END IF
IF( N.EQ.0 )
$ RETURN
NB = ILAENV( 1, 'ZHEGST', UPLO, N, -1, -1, -1 )
IF( NB.LE.1 .OR. NB.GE.N ) THEN
CALL ZHEGS2( ITYPE, UPLO, N, A, LDA, B, LDB, INFO )
ELSE
IF( ITYPE.EQ.1 ) THEN
IF( UPPER ) THEN
DO 10 K = 1, N, NB
KB = MIN( N-K+1, NB )
CALL ZHEGS2( ITYPE, UPLO, KB, A( K, K ), LDA,
$ B( K, K ), LDB, INFO )
IF( K+KB.LE.N ) THEN
CALL ZTRSM( 'Left', UPLO, 'Conjugate transpose',
$ 'Non-unit', KB, N-K-KB+1, CONE,
$ B( K, K ), LDB, A( K, K+KB ), LDA )
CALL ZHEMM( 'Left', UPLO, KB, N-K-KB+1, -HALF,
$ A( K, K ), LDA, B( K, K+KB ), LDB,
$ CONE, A( K, K+KB ), LDA )
CALL ZHER2K( UPLO, 'Conjugate transpose', N-K-KB+1,
$ KB, -CONE, A( K, K+KB ), LDA,
$ B( K, K+KB ), LDB, ONE,
$ A( K+KB, K+KB ), LDA )
CALL ZHEMM( 'Left', UPLO, KB, N-K-KB+1, -HALF,
$ A( K, K ), LDA, B( K, K+KB ), LDB,
$ CONE, A( K, K+KB ), LDA )
CALL ZTRSM( 'Right', UPLO, 'No transpose',
$ 'Non-unit', KB, N-K-KB+1, CONE,
$ B( K+KB, K+KB ), LDB, A( K, K+KB ),
$ LDA )
END IF
10 CONTINUE
ELSE
DO 20 K = 1, N, NB
KB = MIN( N-K+1, NB )
CALL ZHEGS2( ITYPE, UPLO, KB, A( K, K ), LDA,
$ B( K, K ), LDB, INFO )
IF( K+KB.LE.N ) THEN
CALL ZTRSM( 'Right', UPLO, 'Conjugate transpose',
$ 'Non-unit', N-K-KB+1, KB, CONE,
$ B( K, K ), LDB, A( K+KB, K ), LDA )
CALL ZHEMM( 'Right', UPLO, N-K-KB+1, KB, -HALF,
$ A( K, K ), LDA, B( K+KB, K ), LDB,
$ CONE, A( K+KB, K ), LDA )
CALL ZHER2K( UPLO, 'No transpose', N-K-KB+1, KB,
$ -CONE, A( K+KB, K ), LDA,
$ B( K+KB, K ), LDB, ONE,
$ A( K+KB, K+KB ), LDA )
CALL ZHEMM( 'Right', UPLO, N-K-KB+1, KB, -HALF,
$ A( K, K ), LDA, B( K+KB, K ), LDB,
$ CONE, A( K+KB, K ), LDA )
CALL ZTRSM( 'Left', UPLO, 'No transpose',
$ 'Non-unit', N-K-KB+1, KB, CONE,
$ B( K+KB, K+KB ), LDB, A( K+KB, K ),
$ LDA )
END IF
20 CONTINUE
END IF
ELSE
IF( UPPER ) THEN
DO 30 K = 1, N, NB
KB = MIN( N-K+1, NB )
CALL ZTRMM( 'Left', UPLO, 'No transpose', 'Non-unit',
$ K-1, KB, CONE, B, LDB, A( 1, K ), LDA )
CALL ZHEMM( 'Right', UPLO, K-1, KB, HALF, A( K, K ),
$ LDA, B( 1, K ), LDB, CONE, A( 1, K ),
$ LDA )
CALL ZHER2K( UPLO, 'No transpose', K-1, KB, CONE,
$ A( 1, K ), LDA, B( 1, K ), LDB, ONE, A,
$ LDA )
CALL ZHEMM( 'Right', UPLO, K-1, KB, HALF, A( K, K ),
$ LDA, B( 1, K ), LDB, CONE, A( 1, K ),
$ LDA )
CALL ZTRMM( 'Right', UPLO, 'Conjugate transpose',
$ 'Non-unit', K-1, KB, CONE, B( K, K ), LDB,
$ A( 1, K ), LDA )
CALL ZHEGS2( ITYPE, UPLO, KB, A( K, K ), LDA,
$ B( K, K ), LDB, INFO )
30 CONTINUE
ELSE
DO 40 K = 1, N, NB
KB = MIN( N-K+1, NB )
CALL ZTRMM( 'Right', UPLO, 'No transpose', 'Non-unit',
$ KB, K-1, CONE, B, LDB, A( K, 1 ), LDA )
CALL ZHEMM( 'Left', UPLO, KB, K-1, HALF, A( K, K ),
$ LDA, B( K, 1 ), LDB, CONE, A( K, 1 ),
$ LDA )
CALL ZHER2K( UPLO, 'Conjugate transpose', K-1, KB,
$ CONE, A( K, 1 ), LDA, B( K, 1 ), LDB,
$ ONE, A, LDA )
CALL ZHEMM( 'Left', UPLO, KB, K-1, HALF, A( K, K ),
$ LDA, B( K, 1 ), LDB, CONE, A( K, 1 ),
$ LDA )
CALL ZTRMM( 'Left', UPLO, 'Conjugate transpose',
$ 'Non-unit', KB, K-1, CONE, B( K, K ), LDB,
$ A( K, 1 ), LDA )
CALL ZHEGS2( ITYPE, UPLO, KB, A( K, K ), LDA,
$ B( K, K ), LDB, INFO )
40 CONTINUE
END IF
END IF
END IF
RETURN
END