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385 lines
12 KiB
Fortran
385 lines
12 KiB
Fortran
*DECK STRSM
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SUBROUTINE STRSM (SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA,
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$ B, LDB)
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C***BEGIN PROLOGUE STRSM
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C***PURPOSE Solve a real triangular system of equations with multiple
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C right-hand sides.
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C***LIBRARY SLATEC (BLAS)
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C***CATEGORY D1B6
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C***TYPE SINGLE PRECISION (STRSM-S, DTRSM-D, CTRSM-C)
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C***KEYWORDS LEVEL 3 BLAS, LINEAR ALGEBRA
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C***AUTHOR Dongarra, J., (ANL)
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C Duff, I., (AERE)
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C Du Croz, J., (NAG)
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C Hammarling, S. (NAG)
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C***DESCRIPTION
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C
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C STRSM solves one of the matrix equations
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C
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C op( A )*X = alpha*B, or X*op( A ) = alpha*B,
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C
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C where alpha is a scalar, X and B are m by n matrices, A is a unit, or
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C non-unit, upper or lower triangular matrix and op( A ) is one of
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C
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C op( A ) = A or op( A ) = A'.
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C
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C The matrix X is overwritten on B.
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C
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C Parameters
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C ==========
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C
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C SIDE - CHARACTER*1.
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C On entry, SIDE specifies whether op( A ) appears on the left
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C or right of X as follows:
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C
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C SIDE = 'L' or 'l' op( A )*X = alpha*B.
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C
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C SIDE = 'R' or 'r' X*op( A ) = alpha*B.
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C
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C Unchanged on exit.
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C
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C UPLO - CHARACTER*1.
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C On entry, UPLO specifies whether the matrix A is an upper or
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C lower triangular matrix as follows:
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C
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C UPLO = 'U' or 'u' A is an upper triangular matrix.
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C
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C UPLO = 'L' or 'l' A is a lower triangular matrix.
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C
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C Unchanged on exit.
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C
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C TRANSA - CHARACTER*1.
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C On entry, TRANSA specifies the form of op( A ) to be used in
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C the matrix multiplication as follows:
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C
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C TRANSA = 'N' or 'n' op( A ) = A.
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C
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C TRANSA = 'T' or 't' op( A ) = A'.
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C
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C TRANSA = 'C' or 'c' op( A ) = A'.
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C
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C Unchanged on exit.
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C
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C DIAG - CHARACTER*1.
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C On entry, DIAG specifies whether or not A is unit triangular
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C as follows:
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C
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C DIAG = 'U' or 'u' A is assumed to be unit triangular.
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C
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C DIAG = 'N' or 'n' A is not assumed to be unit
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C triangular.
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C
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C Unchanged on exit.
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C
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C M - INTEGER.
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C On entry, M specifies the number of rows of B. M must be at
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C least zero.
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C Unchanged on exit.
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C
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C N - INTEGER.
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C On entry, N specifies the number of columns of B. N must be
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C at least zero.
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C Unchanged on exit.
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C
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C ALPHA - REAL .
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C On entry, ALPHA specifies the scalar alpha. When alpha is
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C zero then A is not referenced and B need not be set before
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C entry.
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C Unchanged on exit.
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C
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C A - REAL array of DIMENSION ( LDA, k ), where k is m
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C when SIDE = 'L' or 'l' and is n when SIDE = 'R' or 'r'.
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C Before entry with UPLO = 'U' or 'u', the leading k by k
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C upper triangular part of the array A must contain the upper
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C triangular matrix and the strictly lower triangular part of
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C A is not referenced.
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C Before entry with UPLO = 'L' or 'l', the leading k by k
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C lower triangular part of the array A must contain the lower
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C triangular matrix and the strictly upper triangular part of
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C A is not referenced.
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C Note that when DIAG = 'U' or 'u', the diagonal elements of
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C A are not referenced either, but are assumed to be unity.
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C Unchanged on exit.
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C
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C LDA - INTEGER.
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C On entry, LDA specifies the first dimension of A as declared
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C in the calling (sub) program. When SIDE = 'L' or 'l' then
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C LDA must be at least max( 1, m ), when SIDE = 'R' or 'r'
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C then LDA must be at least max( 1, n ).
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C Unchanged on exit.
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C
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C B - REAL array of DIMENSION ( LDB, n ).
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C Before entry, the leading m by n part of the array B must
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C contain the right-hand side matrix B, and on exit is
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C overwritten by the solution matrix X.
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C
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C LDB - INTEGER.
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C On entry, LDB specifies the first dimension of B as declared
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C in the calling (sub) program. LDB must be at least
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C max( 1, m ).
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C Unchanged on exit.
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C
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C***REFERENCES Dongarra, J., Du Croz, J., Duff, I., and Hammarling, S.
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C A set of level 3 basic linear algebra subprograms.
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C ACM TOMS, Vol. 16, No. 1, pp. 1-17, March 1990.
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C***ROUTINES CALLED LSAME, XERBLA
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C***REVISION HISTORY (YYMMDD)
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C 890208 DATE WRITTEN
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C 910605 Modified to meet SLATEC prologue standards. Only comment
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C lines were modified. (BKS)
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C***END PROLOGUE STRSM
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C .. Scalar Arguments ..
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CHARACTER*1 SIDE, UPLO, TRANSA, DIAG
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INTEGER M, N, LDA, LDB
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REAL ALPHA
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C .. Array Arguments ..
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REAL A( LDA, * ), B( LDB, * )
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C
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C .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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C .. External Subroutines ..
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EXTERNAL XERBLA
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C .. Intrinsic Functions ..
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INTRINSIC MAX
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C .. Local Scalars ..
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LOGICAL LSIDE, NOUNIT, UPPER
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INTEGER I, INFO, J, K, NROWA
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REAL TEMP
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C .. 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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C***FIRST EXECUTABLE STATEMENT STRSM
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C
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C Test the input parameters.
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C
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LSIDE = LSAME( SIDE , 'L' )
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IF( LSIDE )THEN
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NROWA = M
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ELSE
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NROWA = N
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END IF
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NOUNIT = LSAME( DIAG , 'N' )
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UPPER = LSAME( UPLO , 'U' )
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C
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INFO = 0
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IF( ( .NOT.LSIDE ).AND.
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$ ( .NOT.LSAME( SIDE , 'R' ) ) )THEN
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INFO = 1
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ELSE IF( ( .NOT.UPPER ).AND.
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$ ( .NOT.LSAME( UPLO , 'L' ) ) )THEN
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INFO = 2
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ELSE IF( ( .NOT.LSAME( TRANSA, 'N' ) ).AND.
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$ ( .NOT.LSAME( TRANSA, 'T' ) ).AND.
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$ ( .NOT.LSAME( TRANSA, 'C' ) ) )THEN
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INFO = 3
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ELSE IF( ( .NOT.LSAME( DIAG , 'U' ) ).AND.
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$ ( .NOT.LSAME( DIAG , 'N' ) ) )THEN
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INFO = 4
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ELSE IF( M .LT.0 )THEN
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INFO = 5
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ELSE IF( N .LT.0 )THEN
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INFO = 6
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ELSE IF( LDA.LT.MAX( 1, NROWA ) )THEN
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INFO = 9
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ELSE IF( LDB.LT.MAX( 1, M ) )THEN
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INFO = 11
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END IF
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IF( INFO.NE.0 )THEN
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CALL XERBLA( 'STRSM ', INFO )
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RETURN
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END IF
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C
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C Quick return if possible.
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C
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IF( N.EQ.0 )
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$ RETURN
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C
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C And when alpha.eq.zero.
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C
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IF( ALPHA.EQ.ZERO )THEN
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DO 20, J = 1, N
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DO 10, I = 1, M
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B( I, J ) = ZERO
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10 CONTINUE
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20 CONTINUE
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RETURN
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END IF
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C
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C Start the operations.
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C
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IF( LSIDE )THEN
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IF( LSAME( TRANSA, 'N' ) )THEN
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C
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C Form B := alpha*inv( A )*B.
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C
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IF( UPPER )THEN
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DO 60, J = 1, N
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IF( ALPHA.NE.ONE )THEN
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DO 30, I = 1, M
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B( I, J ) = ALPHA*B( I, J )
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30 CONTINUE
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END IF
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DO 50, K = M, 1, -1
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IF( B( K, J ).NE.ZERO )THEN
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IF( NOUNIT )
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$ B( K, J ) = B( K, J )/A( K, K )
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DO 40, I = 1, K - 1
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B( I, J ) = B( I, J ) - B( K, J )*A( I, K )
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40 CONTINUE
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END IF
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50 CONTINUE
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60 CONTINUE
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ELSE
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DO 100, J = 1, N
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IF( ALPHA.NE.ONE )THEN
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DO 70, I = 1, M
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B( I, J ) = ALPHA*B( I, J )
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70 CONTINUE
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END IF
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DO 90 K = 1, M
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IF( B( K, J ).NE.ZERO )THEN
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IF( NOUNIT )
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$ B( K, J ) = B( K, J )/A( K, K )
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DO 80, I = K + 1, M
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B( I, J ) = B( I, J ) - B( K, J )*A( I, K )
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80 CONTINUE
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END IF
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90 CONTINUE
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100 CONTINUE
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END IF
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ELSE
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C
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C Form B := alpha*inv( A' )*B.
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C
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IF( UPPER )THEN
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DO 130, J = 1, N
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DO 120, I = 1, M
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TEMP = ALPHA*B( I, J )
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DO 110, K = 1, I - 1
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TEMP = TEMP - A( K, I )*B( K, J )
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110 CONTINUE
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IF( NOUNIT )
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$ TEMP = TEMP/A( I, I )
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B( I, J ) = TEMP
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120 CONTINUE
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130 CONTINUE
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ELSE
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DO 160, J = 1, N
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DO 150, I = M, 1, -1
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TEMP = ALPHA*B( I, J )
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DO 140, K = I + 1, M
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TEMP = TEMP - A( K, I )*B( K, J )
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140 CONTINUE
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IF( NOUNIT )
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$ TEMP = TEMP/A( I, I )
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B( I, J ) = TEMP
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150 CONTINUE
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160 CONTINUE
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END IF
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END IF
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ELSE
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IF( LSAME( TRANSA, 'N' ) )THEN
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C
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C Form B := alpha*B*inv( A ).
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C
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IF( UPPER )THEN
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DO 210, J = 1, N
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IF( ALPHA.NE.ONE )THEN
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DO 170, I = 1, M
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B( I, J ) = ALPHA*B( I, J )
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170 CONTINUE
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END IF
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DO 190, K = 1, J - 1
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IF( A( K, J ).NE.ZERO )THEN
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DO 180, I = 1, M
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B( I, J ) = B( I, J ) - A( K, J )*B( I, K )
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180 CONTINUE
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END IF
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190 CONTINUE
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IF( NOUNIT )THEN
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TEMP = ONE/A( J, J )
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DO 200, I = 1, M
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B( I, J ) = TEMP*B( I, J )
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200 CONTINUE
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END IF
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210 CONTINUE
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ELSE
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DO 260, J = N, 1, -1
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IF( ALPHA.NE.ONE )THEN
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DO 220, I = 1, M
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B( I, J ) = ALPHA*B( I, J )
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220 CONTINUE
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END IF
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DO 240, K = J + 1, N
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IF( A( K, J ).NE.ZERO )THEN
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DO 230, I = 1, M
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B( I, J ) = B( I, J ) - A( K, J )*B( I, K )
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230 CONTINUE
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END IF
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240 CONTINUE
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IF( NOUNIT )THEN
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TEMP = ONE/A( J, J )
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DO 250, I = 1, M
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B( I, J ) = TEMP*B( I, J )
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250 CONTINUE
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END IF
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260 CONTINUE
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END IF
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ELSE
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C
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C Form B := alpha*B*inv( A' ).
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C
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IF( UPPER )THEN
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DO 310, K = N, 1, -1
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IF( NOUNIT )THEN
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TEMP = ONE/A( K, K )
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DO 270, I = 1, M
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B( I, K ) = TEMP*B( I, K )
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270 CONTINUE
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END IF
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DO 290, J = 1, K - 1
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IF( A( J, K ).NE.ZERO )THEN
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TEMP = A( J, K )
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DO 280, I = 1, M
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B( I, J ) = B( I, J ) - TEMP*B( I, K )
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280 CONTINUE
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END IF
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290 CONTINUE
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IF( ALPHA.NE.ONE )THEN
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DO 300, I = 1, M
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B( I, K ) = ALPHA*B( I, K )
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300 CONTINUE
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END IF
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310 CONTINUE
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ELSE
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DO 360, K = 1, N
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IF( NOUNIT )THEN
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TEMP = ONE/A( K, K )
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DO 320, I = 1, M
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B( I, K ) = TEMP*B( I, K )
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320 CONTINUE
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END IF
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DO 340, J = K + 1, N
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IF( A( J, K ).NE.ZERO )THEN
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TEMP = A( J, K )
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DO 330, I = 1, M
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B( I, J ) = B( I, J ) - TEMP*B( I, K )
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330 CONTINUE
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END IF
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340 CONTINUE
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IF( ALPHA.NE.ONE )THEN
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DO 350, I = 1, M
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B( I, K ) = ALPHA*B( I, K )
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350 CONTINUE
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END IF
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360 CONTINUE
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END IF
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END IF
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END IF
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C
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RETURN
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C
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C End of STRSM .
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C
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END
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