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SUBROUTINE SSYMM(SIDE,UPLO,M,N,ALPHA,A,LDA,B,LDB,BETA,C,LDC)
* .. Scalar Arguments ..
REAL ALPHA,BETA
INTEGER LDA,LDB,LDC,M,N
CHARACTER SIDE,UPLO
* ..
* .. Array Arguments ..
REAL A(LDA,*),B(LDB,*),C(LDC,*)
* ..
*
* Purpose
* =======
*
* SSYMM 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.
*
* Arguments
* ==========
*
* SIDE - 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,
*
* Unchanged on exit.
*
* UPLO - 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.
*
* Unchanged on exit.
*
* M - INTEGER.
* On entry, M specifies the number of rows of the matrix C.
* M must be at least zero.
* Unchanged on exit.
*
* N - INTEGER.
* On entry, N specifies the number of columns of the matrix C.
* N must be at least zero.
* Unchanged on exit.
*
* ALPHA - REAL .
* On entry, ALPHA specifies the scalar alpha.
* Unchanged on exit.
*
* A - REAL 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.
* Unchanged on exit.
*
* LDA - 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 ).
* Unchanged on exit.
*
* B - REAL array of DIMENSION ( LDB, n ).
* Before entry, the leading m by n part of the array B must
* contain the matrix B.
* Unchanged on exit.
*
* LDB - 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 ).
* Unchanged on exit.
*
* BETA - REAL .
* On entry, BETA specifies the scalar beta. When BETA is
* supplied as zero then C need not be set on input.
* Unchanged on exit.
*
* C - REAL 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.
*
* LDC - 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 ).
* Unchanged on exit.
*
* Further Details
* ===============
*
* 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.
*
* =====================================================================
*
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. External Subroutines ..
EXTERNAL XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX
* ..
* .. Local Scalars ..
REAL TEMP1,TEMP2
INTEGER I,INFO,J,K,NROWA
LOGICAL UPPER
* ..
* .. Parameters ..
REAL ONE,ZERO
PARAMETER (ONE=1.0E+0,ZERO=0.0E+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('SSYMM ',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 SSYMM .
*
END
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