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lammps/lib/linalg/dsymm.f
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dsymm.f
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*> \brief \b DSYMM
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* SUBROUTINE DSYMM(SIDE,UPLO,M,N,ALPHA,A,LDA,B,LDB,BETA,C,LDC)
*
* .. Scalar Arguments ..
* DOUBLE PRECISION ALPHA,BETA
* INTEGER LDA,LDB,LDC,M,N
* CHARACTER SIDE,UPLO
* ..
* .. Array Arguments ..
* DOUBLE PRECISION A(LDA,*),B(LDB,*),C(LDC,*)
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> DSYMM performs one of the matrix-matrix operations
*>
*> C := alpha*A*B + beta*C,
*>
*> or
*>
*> C := alpha*B*A + beta*C,
*>
*> where alpha and beta are scalars, A is a symmetric matrix and B and
*> C are m by n matrices.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] SIDE
*> \verbatim
*> SIDE is CHARACTER*1
*> On entry, SIDE specifies whether the symmetric matrix A
*> appears on the left or right in the operation as follows:
*>
*> SIDE = 'L' or 'l' C := alpha*A*B + beta*C,
*>
*> SIDE = 'R' or 'r' C := alpha*B*A + beta*C,
*> \endverbatim
*>
*> \param[in] UPLO
*> \verbatim
*> UPLO is CHARACTER*1
*> On entry, UPLO specifies whether the upper or lower
*> triangular part of the symmetric matrix A is to be
*> referenced as follows:
*>
*> UPLO = 'U' or 'u' Only the upper triangular part of the
*> symmetric matrix is to be referenced.
*>
*> UPLO = 'L' or 'l' Only the lower triangular part of the
*> symmetric matrix is to be referenced.
*> \endverbatim
*>
*> \param[in] M
*> \verbatim
*> M is INTEGER
*> On entry, M specifies the number of rows of the matrix C.
*> M must be at least zero.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> On entry, N specifies the number of columns of the matrix C.
*> N must be at least zero.
*> \endverbatim
*>
*> \param[in] ALPHA
*> \verbatim
*> ALPHA is DOUBLE PRECISION.
*> On entry, ALPHA specifies the scalar alpha.
*> \endverbatim
*>
*> \param[in] A
*> \verbatim
*> A is DOUBLE PRECISION array of DIMENSION ( LDA, ka ), where ka is
*> m when SIDE = 'L' or 'l' and is n otherwise.
*> Before entry with SIDE = 'L' or 'l', the m by m part of
*> the array A must contain the symmetric matrix, such that
*> when UPLO = 'U' or 'u', the leading m by m upper triangular
*> part of the array A must contain the upper triangular part
*> of the symmetric matrix and the strictly lower triangular
*> part of A is not referenced, and when UPLO = 'L' or 'l',
*> the leading m by m lower triangular part of the array A
*> must contain the lower triangular part of the symmetric
*> matrix and the strictly upper triangular part of A is not
*> referenced.
*> Before entry with SIDE = 'R' or 'r', the n by n part of
*> the array A must contain the symmetric matrix, such that
*> when UPLO = 'U' or 'u', the leading n by n upper triangular
*> part of the array A must contain the upper triangular part
*> of the symmetric matrix and the strictly lower triangular
*> part of A is not referenced, and when UPLO = 'L' or 'l',
*> the leading n by n lower triangular part of the array A
*> must contain the lower triangular part of the symmetric
*> matrix and the strictly upper triangular part of A is not
*> referenced.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*> LDA is INTEGER
*> On entry, LDA specifies the first dimension of A as declared
*> in the calling (sub) program. When SIDE = 'L' or 'l' then
*> LDA must be at least max( 1, m ), otherwise LDA must be at
*> least max( 1, n ).
*> \endverbatim
*>
*> \param[in] B
*> \verbatim
*> B is DOUBLE PRECISION array of DIMENSION ( LDB, n ).
*> Before entry, the leading m by n part of the array B must
*> contain the matrix B.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*> LDB is INTEGER
*> On entry, LDB specifies the first dimension of B as declared
*> in the calling (sub) program. LDB must be at least
*> max( 1, m ).
*> \endverbatim
*>
*> \param[in] BETA
*> \verbatim
*> BETA is DOUBLE PRECISION.
*> On entry, BETA specifies the scalar beta. When BETA is
*> supplied as zero then C need not be set on input.
*> \endverbatim
*>
*> \param[in,out] C
*> \verbatim
*> C is DOUBLE PRECISION array of DIMENSION ( LDC, n ).
*> Before entry, the leading m by n part of the array C must
*> contain the matrix C, except when beta is zero, in which
*> case C need not be set on entry.
*> On exit, the array C is overwritten by the m by n updated
*> matrix.
*> \endverbatim
*>
*> \param[in] LDC
*> \verbatim
*> LDC is INTEGER
*> On entry, LDC specifies the first dimension of C as declared
*> in the calling (sub) program. LDC must be at least
*> max( 1, m ).
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date November 2011
*
*> \ingroup double_blas_level3
*
*> \par Further Details:
* =====================
*>
*> \verbatim
*>
*> Level 3 Blas routine.
*>
*> -- Written on 8-February-1989.
*> Jack Dongarra, Argonne National Laboratory.
*> Iain Duff, AERE Harwell.
*> Jeremy Du Croz, Numerical Algorithms Group Ltd.
*> Sven Hammarling, Numerical Algorithms Group Ltd.
*> \endverbatim
*>
* =====================================================================
SUBROUTINE DSYMM(SIDE,UPLO,M,N,ALPHA,A,LDA,B,LDB,BETA,C,LDC)
*
* -- Reference BLAS level3 routine (version 3.4.0) --
* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* November 2011
*
* .. Scalar Arguments ..
DOUBLE PRECISION ALPHA,BETA
INTEGER LDA,LDB,LDC,M,N
CHARACTER SIDE,UPLO
* ..
* .. Array Arguments ..
DOUBLE PRECISION A(LDA,*),B(LDB,*),C(LDC,*)
* ..
*
* =====================================================================
*
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. External Subroutines ..
EXTERNAL XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX
* ..
* .. Local Scalars ..
DOUBLE PRECISION TEMP1,TEMP2
INTEGER I,INFO,J,K,NROWA
LOGICAL UPPER
* ..
* .. Parameters ..
DOUBLE PRECISION ONE,ZERO
PARAMETER (ONE=1.0D+0,ZERO=0.0D+0)
* ..
*
* Set NROWA as the number of rows of A.
*
IF (LSAME(SIDE,'L')) THEN
NROWA = M
ELSE
NROWA = N
END IF
UPPER = LSAME(UPLO,'U')
*
* Test the input parameters.
*
INFO = 0
IF ((.NOT.LSAME(SIDE,'L')) .AND. (.NOT.LSAME(SIDE,'R'))) THEN
INFO = 1
ELSE IF ((.NOT.UPPER) .AND. (.NOT.LSAME(UPLO,'L'))) THEN
INFO = 2
ELSE IF (M.LT.0) THEN
INFO = 3
ELSE IF (N.LT.0) THEN
INFO = 4
ELSE IF (LDA.LT.MAX(1,NROWA)) THEN
INFO = 7
ELSE IF (LDB.LT.MAX(1,M)) THEN
INFO = 9
ELSE IF (LDC.LT.MAX(1,M)) THEN
INFO = 12
END IF
IF (INFO.NE.0) THEN
CALL XERBLA('DSYMM ',INFO)
RETURN
END IF
*
* Quick return if possible.
*
IF ((M.EQ.0) .OR. (N.EQ.0) .OR.
+ ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN
*
* And when alpha.eq.zero.
*
IF (ALPHA.EQ.ZERO) THEN
IF (BETA.EQ.ZERO) THEN
DO 20 J = 1,N
DO 10 I = 1,M
C(I,J) = ZERO
10 CONTINUE
20 CONTINUE
ELSE
DO 40 J = 1,N
DO 30 I = 1,M
C(I,J) = BETA*C(I,J)
30 CONTINUE
40 CONTINUE
END IF
RETURN
END IF
*
* Start the operations.
*
IF (LSAME(SIDE,'L')) THEN
*
* Form C := alpha*A*B + beta*C.
*
IF (UPPER) THEN
DO 70 J = 1,N
DO 60 I = 1,M
TEMP1 = ALPHA*B(I,J)
TEMP2 = ZERO
DO 50 K = 1,I - 1
C(K,J) = C(K,J) + TEMP1*A(K,I)
TEMP2 = TEMP2 + B(K,J)*A(K,I)
50 CONTINUE
IF (BETA.EQ.ZERO) THEN
C(I,J) = TEMP1*A(I,I) + ALPHA*TEMP2
ELSE
C(I,J) = BETA*C(I,J) + TEMP1*A(I,I) +
+ ALPHA*TEMP2
END IF
60 CONTINUE
70 CONTINUE
ELSE
DO 100 J = 1,N
DO 90 I = M,1,-1
TEMP1 = ALPHA*B(I,J)
TEMP2 = ZERO
DO 80 K = I + 1,M
C(K,J) = C(K,J) + TEMP1*A(K,I)
TEMP2 = TEMP2 + B(K,J)*A(K,I)
80 CONTINUE
IF (BETA.EQ.ZERO) THEN
C(I,J) = TEMP1*A(I,I) + ALPHA*TEMP2
ELSE
C(I,J) = BETA*C(I,J) + TEMP1*A(I,I) +
+ ALPHA*TEMP2
END IF
90 CONTINUE
100 CONTINUE
END IF
ELSE
*
* Form C := alpha*B*A + beta*C.
*
DO 170 J = 1,N
TEMP1 = ALPHA*A(J,J)
IF (BETA.EQ.ZERO) THEN
DO 110 I = 1,M
C(I,J) = TEMP1*B(I,J)
110 CONTINUE
ELSE
DO 120 I = 1,M
C(I,J) = BETA*C(I,J) + TEMP1*B(I,J)
120 CONTINUE
END IF
DO 140 K = 1,J - 1
IF (UPPER) THEN
TEMP1 = ALPHA*A(K,J)
ELSE
TEMP1 = ALPHA*A(J,K)
END IF
DO 130 I = 1,M
C(I,J) = C(I,J) + TEMP1*B(I,K)
130 CONTINUE
140 CONTINUE
DO 160 K = J + 1,N
IF (UPPER) THEN
TEMP1 = ALPHA*A(J,K)
ELSE
TEMP1 = ALPHA*A(K,J)
END IF
DO 150 I = 1,M
C(I,J) = C(I,J) + TEMP1*B(I,K)
150 CONTINUE
160 CONTINUE
170 CONTINUE
END IF
*
RETURN
*
* End of DSYMM .
*
END
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