327 lines
11 KiB
Fortran
327 lines
11 KiB
Fortran
SUBROUTINE SSYR2KF( UPLO, TRANS, N, K, ALPHA, A, LDA, B, LDB,
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$ BETA, C, LDC )
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* .. Scalar Arguments ..
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CHARACTER*1 UPLO, TRANS
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INTEGER N, K, LDA, LDB, LDC
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REAL ALPHA, BETA
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* .. Array Arguments ..
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REAL A( LDA, * ), B( LDB, * ), C( LDC, * )
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* ..
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*
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* Purpose
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* =======
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*
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* SSYR2K performs one of the symmetric rank 2k operations
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*
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* C := alpha*A*B' + alpha*B*A' + beta*C,
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*
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* or
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*
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* C := alpha*A'*B + alpha*B'*A + beta*C,
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*
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* where alpha and beta are scalars, C is an n by n symmetric matrix
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* and A and B are n by k matrices in the first case and k by n
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* matrices in the second case.
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*
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* Parameters
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* ==========
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*
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* UPLO - CHARACTER*1.
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* On entry, UPLO specifies whether the upper or lower
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* triangular part of the array C is to be referenced as
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* follows:
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*
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* UPLO = 'U' or 'u' Only the upper triangular part of C
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* is to be referenced.
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*
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* UPLO = 'L' or 'l' Only the lower triangular part of C
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* is to be referenced.
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*
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* Unchanged on exit.
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*
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* TRANS - CHARACTER*1.
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* On entry, TRANS specifies the operation to be performed as
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* follows:
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*
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* TRANS = 'N' or 'n' C := alpha*A*B' + alpha*B*A' +
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* beta*C.
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*
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* TRANS = 'T' or 't' C := alpha*A'*B + alpha*B'*A +
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* beta*C.
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*
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* TRANS = 'C' or 'c' C := alpha*A'*B + alpha*B'*A +
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* beta*C.
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*
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* Unchanged on exit.
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*
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* N - INTEGER.
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* On entry, N specifies the order of the matrix C. N must be
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* at least zero.
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* Unchanged on exit.
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*
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* K - INTEGER.
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* On entry with TRANS = 'N' or 'n', K specifies the number
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* of columns of the matrices A and B, and on entry with
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* TRANS = 'T' or 't' or 'C' or 'c', K specifies the number
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* of rows of the matrices A and B. K must be at least zero.
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* Unchanged on exit.
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*
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* ALPHA - REAL .
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* On entry, ALPHA specifies the scalar alpha.
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* Unchanged on exit.
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*
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* A - REAL array of DIMENSION ( LDA, ka ), where ka is
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* k when TRANS = 'N' or 'n', and is n otherwise.
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* Before entry with TRANS = 'N' or 'n', the leading n by k
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* part of the array A must contain the matrix A, otherwise
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* the leading k by n part of the array A must contain the
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* matrix A.
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* Unchanged on exit.
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*
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* LDA - INTEGER.
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* On entry, LDA specifies the first dimension of A as declared
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* in the calling (sub) program. When TRANS = 'N' or 'n'
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* then LDA must be at least max( 1, n ), otherwise LDA must
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* be at least max( 1, k ).
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* Unchanged on exit.
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*
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* B - REAL array of DIMENSION ( LDB, kb ), where kb is
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* k when TRANS = 'N' or 'n', and is n otherwise.
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* Before entry with TRANS = 'N' or 'n', the leading n by k
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* part of the array B must contain the matrix B, otherwise
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* the leading k by n part of the array B must contain the
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* matrix B.
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* Unchanged on exit.
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*
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* LDB - INTEGER.
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* On entry, LDB specifies the first dimension of B as declared
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* in the calling (sub) program. When TRANS = 'N' or 'n'
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* then LDB must be at least max( 1, n ), otherwise LDB must
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* be at least max( 1, k ).
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* Unchanged on exit.
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*
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* BETA - REAL .
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* On entry, BETA specifies the scalar beta.
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* Unchanged on exit.
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*
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* C - REAL array of DIMENSION ( LDC, n ).
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* Before entry with UPLO = 'U' or 'u', the leading n by n
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* upper triangular part of the array C must contain the upper
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* triangular part of the symmetric matrix and the strictly
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* lower triangular part of C is not referenced. On exit, the
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* upper triangular part of the array C is overwritten by the
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* upper triangular part of the updated matrix.
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* Before entry with UPLO = 'L' or 'l', the leading n by n
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* lower triangular part of the array C must contain the lower
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* triangular part of the symmetric matrix and the strictly
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* upper triangular part of C is not referenced. On exit, the
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* lower triangular part of the array C is overwritten by the
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* lower triangular part of the updated matrix.
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*
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* LDC - INTEGER.
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* On entry, LDC specifies the first dimension of C as declared
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* in the calling (sub) program. LDC must be at least
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* max( 1, n ).
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* Unchanged on exit.
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*
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*
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* Level 3 Blas routine.
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*
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*
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* -- Written on 8-February-1989.
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* Jack Dongarra, Argonne National Laboratory.
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* Iain Duff, AERE Harwell.
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* Jeremy Du Croz, Numerical Algorithms Group Ltd.
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* Sven Hammarling, Numerical Algorithms Group Ltd.
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*
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*
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* .. External Subroutines ..
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EXTERNAL XERBLA
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* .. Local Scalars ..
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LOGICAL UPPER
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INTEGER I, INFO, J, L, NROWA
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REAL TEMP1, TEMP2
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* .. Parameters ..
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REAL ONE , ZERO
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PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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IF( LSAME( TRANS, 'N' ) )THEN
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NROWA = N
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ELSE
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NROWA = K
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END IF
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UPPER = LSAME( UPLO, 'U' )
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*
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INFO = 0
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IF( ( .NOT.UPPER ).AND.
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$ ( .NOT.LSAME( UPLO , 'L' ) ) )THEN
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INFO = 1
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ELSE IF( ( .NOT.LSAME( TRANS, 'N' ) ).AND.
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$ ( .NOT.LSAME( TRANS, 'T' ) ).AND.
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$ ( .NOT.LSAME( TRANS, 'C' ) ) )THEN
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INFO = 2
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ELSE IF( N .LT.0 )THEN
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INFO = 3
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ELSE IF( K .LT.0 )THEN
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INFO = 4
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ELSE IF( LDA.LT.MAX( 1, NROWA ) )THEN
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INFO = 7
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ELSE IF( LDB.LT.MAX( 1, NROWA ) )THEN
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INFO = 9
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ELSE IF( LDC.LT.MAX( 1, N ) )THEN
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INFO = 12
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END IF
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IF( INFO.NE.0 )THEN
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CALL XERBLA( 'SSYR2K', INFO )
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RETURN
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END IF
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*
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* Quick return if possible.
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*
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IF( ( N.EQ.0 ).OR.
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$ ( ( ( ALPHA.EQ.ZERO ).OR.( K.EQ.0 ) ).AND.( BETA.EQ.ONE ) ) )
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$ RETURN
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*
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* And when alpha.eq.zero.
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*
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IF( ALPHA.EQ.ZERO )THEN
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IF( UPPER )THEN
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IF( BETA.EQ.ZERO )THEN
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DO 20, J = 1, N
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DO 10, I = 1, J
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C( I, J ) = ZERO
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10 CONTINUE
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20 CONTINUE
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ELSE
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DO 40, J = 1, N
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DO 30, I = 1, J
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C( I, J ) = BETA*C( I, J )
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30 CONTINUE
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40 CONTINUE
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END IF
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ELSE
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IF( BETA.EQ.ZERO )THEN
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DO 60, J = 1, N
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DO 50, I = J, N
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C( I, J ) = ZERO
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50 CONTINUE
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60 CONTINUE
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ELSE
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DO 80, J = 1, N
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DO 70, I = J, N
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C( I, J ) = BETA*C( I, J )
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70 CONTINUE
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80 CONTINUE
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END IF
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END IF
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RETURN
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END IF
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*
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* Start the operations.
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*
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IF( LSAME( TRANS, 'N' ) )THEN
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*
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* Form C := alpha*A*B' + alpha*B*A' + C.
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*
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IF( UPPER )THEN
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DO 130, J = 1, N
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IF( BETA.EQ.ZERO )THEN
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DO 90, I = 1, J
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C( I, J ) = ZERO
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90 CONTINUE
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ELSE IF( BETA.NE.ONE )THEN
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DO 100, I = 1, J
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C( I, J ) = BETA*C( I, J )
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100 CONTINUE
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END IF
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DO 120, L = 1, K
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IF( ( A( J, L ).NE.ZERO ).OR.
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$ ( B( J, L ).NE.ZERO ) )THEN
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TEMP1 = ALPHA*B( J, L )
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TEMP2 = ALPHA*A( J, L )
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DO 110, I = 1, J
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C( I, J ) = C( I, J ) +
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$ A( I, L )*TEMP1 + B( I, L )*TEMP2
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110 CONTINUE
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END IF
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120 CONTINUE
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130 CONTINUE
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ELSE
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DO 180, J = 1, N
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IF( BETA.EQ.ZERO )THEN
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DO 140, I = J, N
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C( I, J ) = ZERO
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140 CONTINUE
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ELSE IF( BETA.NE.ONE )THEN
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DO 150, I = J, N
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C( I, J ) = BETA*C( I, J )
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150 CONTINUE
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END IF
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DO 170, L = 1, K
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IF( ( A( J, L ).NE.ZERO ).OR.
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$ ( B( J, L ).NE.ZERO ) )THEN
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TEMP1 = ALPHA*B( J, L )
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TEMP2 = ALPHA*A( J, L )
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DO 160, I = J, N
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C( I, J ) = C( I, J ) +
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$ A( I, L )*TEMP1 + B( I, L )*TEMP2
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160 CONTINUE
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END IF
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170 CONTINUE
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180 CONTINUE
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END IF
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ELSE
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*
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* Form C := alpha*A'*B + alpha*B'*A + C.
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*
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IF( UPPER )THEN
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DO 210, J = 1, N
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DO 200, I = 1, J
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TEMP1 = ZERO
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TEMP2 = ZERO
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DO 190, L = 1, K
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TEMP1 = TEMP1 + A( L, I )*B( L, J )
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TEMP2 = TEMP2 + B( L, I )*A( L, J )
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190 CONTINUE
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IF( BETA.EQ.ZERO )THEN
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C( I, J ) = ALPHA*TEMP1 + ALPHA*TEMP2
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ELSE
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C( I, J ) = BETA *C( I, J ) +
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$ ALPHA*TEMP1 + ALPHA*TEMP2
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END IF
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200 CONTINUE
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210 CONTINUE
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ELSE
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DO 240, J = 1, N
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DO 230, I = J, N
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TEMP1 = ZERO
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TEMP2 = ZERO
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DO 220, L = 1, K
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TEMP1 = TEMP1 + A( L, I )*B( L, J )
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TEMP2 = TEMP2 + B( L, I )*A( L, J )
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220 CONTINUE
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IF( BETA.EQ.ZERO )THEN
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C( I, J ) = ALPHA*TEMP1 + ALPHA*TEMP2
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ELSE
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C( I, J ) = BETA *C( I, J ) +
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$ ALPHA*TEMP1 + ALPHA*TEMP2
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END IF
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230 CONTINUE
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240 CONTINUE
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END IF
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END IF
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*
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RETURN
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*
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* End of SSYR2K.
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*
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END
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