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SUBROUTINE MB01RX( SIDE, UPLO, TRANS, M, N, ALPHA, BETA, R, LDR,
$ A, LDA, B, LDB, INFO )
C
C SLICOT RELEASE 5.0.
C
C Copyright (c) 2002-2009 NICONET e.V.
C
C This program is free software: you can redistribute it and/or
C modify it under the terms of the GNU General Public License as
C published by the Free Software Foundation, either version 2 of
C the License, or (at your option) any later version.
C
C This program is distributed in the hope that it will be useful,
C but WITHOUT ANY WARRANTY; without even the implied warranty of
C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
C GNU General Public License for more details.
C
C You should have received a copy of the GNU General Public License
C along with this program. If not, see
C <http://www.gnu.org/licenses/>.
C
C PURPOSE
C
C To compute either the upper or lower triangular part of one of the
C matrix formulas
C _
C R = alpha*R + beta*op( A )*B, (1)
C _
C R = alpha*R + beta*B*op( A ), (2)
C _
C where alpha and beta are scalars, R and R are m-by-m matrices,
C op( A ) and B are m-by-n and n-by-m matrices for (1), or n-by-m
C and m-by-n matrices for (2), respectively, and op( A ) is one of
C
C op( A ) = A or op( A ) = A', the transpose of A.
C
C The result is overwritten on R.
C
C ARGUMENTS
C
C Mode Parameters
C
C SIDE CHARACTER*1
C Specifies whether the matrix A appears on the left or
C right in the matrix product as follows:
C _
C = 'L': R = alpha*R + beta*op( A )*B;
C _
C = 'R': R = alpha*R + beta*B*op( A ).
C
C UPLO CHARACTER*1 _
C Specifies which triangles of the matrices R and R are
C computed and given, respectively, as follows:
C = 'U': the upper triangular part;
C = 'L': the lower triangular part.
C
C TRANS CHARACTER*1
C Specifies the form of op( A ) to be used in the matrix
C multiplication as follows:
C = 'N': op( A ) = A;
C = 'T': op( A ) = A';
C = 'C': op( A ) = A'.
C
C Input/Output Parameters
C
C M (input) INTEGER _
C The order of the matrices R and R, the number of rows of
C the matrix op( A ) and the number of columns of the
C matrix B, for SIDE = 'L', or the number of rows of the
C matrix B and the number of columns of the matrix op( A ),
C for SIDE = 'R'. M >= 0.
C
C N (input) INTEGER
C The number of rows of the matrix B and the number of
C columns of the matrix op( A ), for SIDE = 'L', or the
C number of rows of the matrix op( A ) and the number of
C columns of the matrix B, for SIDE = 'R'. N >= 0.
C
C ALPHA (input) DOUBLE PRECISION
C The scalar alpha. When alpha is zero then R need not be
C set before entry.
C
C BETA (input) DOUBLE PRECISION
C The scalar beta. When beta is zero then A and B are not
C referenced.
C
C R (input/output) DOUBLE PRECISION array, dimension (LDR,M)
C On entry with UPLO = 'U', the leading M-by-M upper
C triangular part of this array must contain the upper
C triangular part of the matrix R; the strictly lower
C triangular part of the array is not referenced.
C On entry with UPLO = 'L', the leading M-by-M lower
C triangular part of this array must contain the lower
C triangular part of the matrix R; the strictly upper
C triangular part of the array is not referenced.
C On exit, the leading M-by-M upper triangular part (if
C UPLO = 'U'), or lower triangular part (if UPLO = 'L') of
C this array contains the corresponding triangular part of
C _
C the computed matrix R.
C
C LDR INTEGER
C The leading dimension of array R. LDR >= MAX(1,M).
C
C A (input) DOUBLE PRECISION array, dimension (LDA,k), where
C k = N when SIDE = 'L', and TRANS = 'N', or
C SIDE = 'R', and TRANS = 'T';
C k = M when SIDE = 'R', and TRANS = 'N', or
C SIDE = 'L', and TRANS = 'T'.
C On entry, if SIDE = 'L', and TRANS = 'N', or
C SIDE = 'R', and TRANS = 'T',
C the leading M-by-N part of this array must contain the
C matrix A.
C On entry, if SIDE = 'R', and TRANS = 'N', or
C SIDE = 'L', and TRANS = 'T',
C the leading N-by-M part of this array must contain the
C matrix A.
C
C LDA INTEGER
C The leading dimension of array A. LDA >= MAX(1,l), where
C l = M when SIDE = 'L', and TRANS = 'N', or
C SIDE = 'R', and TRANS = 'T';
C l = N when SIDE = 'R', and TRANS = 'N', or
C SIDE = 'L', and TRANS = 'T'.
C
C B (input) DOUBLE PRECISION array, dimension (LDB,p), where
C p = M when SIDE = 'L';
C p = N when SIDE = 'R'.
C On entry, the leading N-by-M part, if SIDE = 'L', or
C M-by-N part, if SIDE = 'R', of this array must contain the
C matrix B.
C
C LDB INTEGER
C The leading dimension of array B.
C LDB >= MAX(1,N), if SIDE = 'L';
C LDB >= MAX(1,M), if SIDE = 'R'.
C
C Error Indicator
C
C INFO INTEGER
C = 0: successful exit;
C < 0: if INFO = -i, the i-th argument had an illegal
C value.
C
C METHOD
C
C The matrix expression is evaluated taking the triangular
C structure into account. BLAS 2 operations are used. A block
C algorithm can be easily constructed; it can use BLAS 3 GEMM
C operations for most computations, and calls of this BLAS 2
C algorithm for computing the triangles.
C
C FURTHER COMMENTS
C
C The main application of this routine is when the result should
C be a symmetric matrix, e.g., when B = X*op( A )', for (1), or
C B = op( A )'*X, for (2), where B is already available and X = X'.
C
C CONTRIBUTORS
C
C V. Sima, Katholieke Univ. Leuven, Belgium, Feb. 1999.
C
C REVISIONS
C
C V. Sima, Research Institute for Informatics, Bucharest, Mar. 2004.
C
C KEYWORDS
C
C Elementary matrix operations, matrix algebra, matrix operations.
C
C ******************************************************************
C
C .. Parameters ..
DOUBLE PRECISION ZERO, ONE
PARAMETER ( ZERO = 0.0D0, ONE = 1.0D0 )
C .. Scalar Arguments ..
CHARACTER SIDE, TRANS, UPLO
INTEGER INFO, LDA, LDB, LDR, M, N
DOUBLE PRECISION ALPHA, BETA
C .. Array Arguments ..
DOUBLE PRECISION A(LDA,*), B(LDB,*), R(LDR,*)
C .. Local Scalars ..
LOGICAL LSIDE, LTRANS, LUPLO
INTEGER J
C .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
C .. External Subroutines ..
EXTERNAL DGEMV, DLASCL, DLASET, XERBLA
C .. Intrinsic Functions ..
INTRINSIC MAX
C .. Executable Statements ..
C
C Test the input scalar arguments.
C
INFO = 0
LSIDE = LSAME( SIDE, 'L' )
LUPLO = LSAME( UPLO, 'U' )
LTRANS = LSAME( TRANS, 'T' ) .OR. LSAME( TRANS, 'C' )
C
IF( ( .NOT.LSIDE ).AND.( .NOT.LSAME( SIDE, 'R' ) ) )THEN
INFO = -1
ELSE IF( ( .NOT.LUPLO ).AND.( .NOT.LSAME( UPLO, 'L' ) ) )THEN
INFO = -2
ELSE IF( ( .NOT.LTRANS ).AND.( .NOT.LSAME( TRANS, 'N' ) ) )THEN
INFO = -3
ELSE IF( M.LT.0 ) THEN
INFO = -4
ELSE IF( N.LT.0 ) THEN
INFO = -5
ELSE IF( LDR.LT.MAX( 1, M ) ) THEN
INFO = -9
ELSE IF( LDA.LT.1 .OR.
$ ( ( ( LSIDE .AND. .NOT.LTRANS ) .OR.
$ ( .NOT.LSIDE .AND. LTRANS ) ) .AND. LDA.LT.M ) .OR.
$ ( ( ( LSIDE .AND. LTRANS ) .OR.
$ ( .NOT.LSIDE .AND. .NOT.LTRANS ) ) .AND. LDA.LT.N ) ) THEN
INFO = -11
ELSE IF( LDB.LT.1 .OR.
$ ( LSIDE .AND. LDB.LT.N ) .OR.
$ ( .NOT.LSIDE .AND. LDB.LT.M ) ) THEN
INFO = -13
END IF
C
IF ( INFO.NE.0 ) THEN
C
C Error return.
C
CALL XERBLA( 'MB01RX', -INFO )
RETURN
END IF
C
C Quick return if possible.
C
IF ( M.EQ.0 )
$ RETURN
C
IF ( BETA.EQ.ZERO .OR. N.EQ.0 ) THEN
IF ( ALPHA.EQ.ZERO ) THEN
C
C Special case alpha = 0.
C
CALL DLASET( UPLO, M, M, ZERO, ZERO, R, LDR )
ELSE
C
C Special case beta = 0 or N = 0.
C
IF ( ALPHA.NE.ONE )
$ CALL DLASCL( UPLO, 0, 0, ONE, ALPHA, M, M, R, LDR, INFO )
END IF
RETURN
END IF
C
C General case: beta <> 0.
C Compute the required triangle of (1) or (2) using BLAS 2
C operations.
C
IF( LSIDE ) THEN
IF( LUPLO ) THEN
IF ( LTRANS ) THEN
DO 10 J = 1, M
CALL DGEMV( TRANS, N, J, BETA, A, LDA, B(1,J), 1,
$ ALPHA, R(1,J), 1 )
10 CONTINUE
ELSE
DO 20 J = 1, M
CALL DGEMV( TRANS, J, N, BETA, A, LDA, B(1,J), 1,
$ ALPHA, R(1,J), 1 )
20 CONTINUE
END IF
ELSE
IF ( LTRANS ) THEN
DO 30 J = 1, M
CALL DGEMV( TRANS, N, M-J+1, BETA, A(1,J), LDA,
$ B(1,J), 1, ALPHA, R(J,J), 1 )
30 CONTINUE
ELSE
DO 40 J = 1, M
CALL DGEMV( TRANS, M-J+1, N, BETA, A(J,1), LDA,
$ B(1,J), 1, ALPHA, R(J,J), 1 )
40 CONTINUE
END IF
END IF
C
ELSE
IF( LUPLO ) THEN
IF( LTRANS ) THEN
DO 50 J = 1, M
CALL DGEMV( 'NoTranspose', J, N, BETA, B, LDB, A(J,1),
$ LDA, ALPHA, R(1,J), 1 )
50 CONTINUE
ELSE
DO 60 J = 1, M
CALL DGEMV( 'NoTranspose', J, N, BETA, B, LDB, A(1,J),
$ 1, ALPHA, R(1,J), 1 )
60 CONTINUE
END IF
ELSE
IF( LTRANS ) THEN
DO 70 J = 1, M
CALL DGEMV( 'NoTranspose', M-J+1, N, BETA, B(J,1),
$ LDB, A(J,1), LDA, ALPHA, R(J,J), 1 )
70 CONTINUE
ELSE
DO 80 J = 1, M
CALL DGEMV( 'NoTranspose', M-J+1, N, BETA, B(J,1),
$ LDB, A(1,J), 1, ALPHA, R(J,J), 1 )
80 CONTINUE
END IF
END IF
END IF
C
RETURN
C *** Last line of MB01RX ***
END
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