forked from lijiext/lammps
282 lines
8.5 KiB
Fortran
282 lines
8.5 KiB
Fortran
SUBROUTINE DTRMV(UPLO,TRANS,DIAG,N,A,LDA,X,INCX)
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* .. Scalar Arguments ..
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INTEGER INCX,LDA,N
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CHARACTER DIAG,TRANS,UPLO
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION A(LDA,*),X(*)
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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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* DTRMV performs one of the matrix-vector operations
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*
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* x := A*x, or x := A'*x,
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*
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* where x is an n element vector and A is an n by n unit, or non-unit,
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* upper or lower triangular matrix.
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*
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* Arguments
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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 matrix is an upper or
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* lower triangular matrix as follows:
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*
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* UPLO = 'U' or 'u' A is an upper triangular matrix.
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*
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* UPLO = 'L' or 'l' A is a lower triangular matrix.
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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' x := A*x.
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*
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* TRANS = 'T' or 't' x := A'*x.
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*
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* TRANS = 'C' or 'c' x := A'*x.
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*
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* Unchanged on exit.
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*
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* DIAG - CHARACTER*1.
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* On entry, DIAG specifies whether or not A is unit
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* triangular as follows:
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*
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* DIAG = 'U' or 'u' A is assumed to be unit triangular.
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*
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* DIAG = 'N' or 'n' A is not assumed to be unit
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* triangular.
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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 A.
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* N must be at least zero.
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* Unchanged on exit.
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*
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* A - DOUBLE PRECISION array of DIMENSION ( LDA, 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 A must contain the upper
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* triangular matrix and the strictly lower triangular part of
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* A is not referenced.
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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 A must contain the lower
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* triangular matrix and the strictly upper triangular part of
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* A is not referenced.
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* Note that when DIAG = 'U' or 'u', the diagonal elements of
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* A are not referenced either, but are assumed to be unity.
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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. LDA 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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* X - DOUBLE PRECISION array of dimension at least
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* ( 1 + ( n - 1 )*abs( INCX ) ).
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* Before entry, the incremented array X must contain the n
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* element vector x. On exit, X is overwritten with the
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* tranformed vector x.
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*
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* INCX - INTEGER.
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* On entry, INCX specifies the increment for the elements of
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* X. INCX must not be zero.
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* Unchanged on exit.
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*
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* Further Details
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* ===============
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*
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* Level 2 Blas routine.
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*
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* -- Written on 22-October-1986.
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* Jack Dongarra, Argonne National Lab.
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* Jeremy Du Croz, Nag Central Office.
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* Sven Hammarling, Nag Central Office.
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* Richard Hanson, Sandia National Labs.
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER (ZERO=0.0D+0)
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* ..
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* .. Local Scalars ..
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DOUBLE PRECISION TEMP
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INTEGER I,INFO,IX,J,JX,KX
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LOGICAL NOUNIT
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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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* ..
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* .. External Subroutines ..
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EXTERNAL XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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*
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* Test the input parameters.
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*
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INFO = 0
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IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
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INFO = 1
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ELSE IF (.NOT.LSAME(TRANS,'N') .AND. .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 (.NOT.LSAME(DIAG,'U') .AND. .NOT.LSAME(DIAG,'N')) THEN
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INFO = 3
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ELSE IF (N.LT.0) THEN
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INFO = 4
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ELSE IF (LDA.LT.MAX(1,N)) THEN
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INFO = 6
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ELSE IF (INCX.EQ.0) THEN
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INFO = 8
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END IF
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IF (INFO.NE.0) THEN
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CALL XERBLA('DTRMV ',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) RETURN
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*
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NOUNIT = LSAME(DIAG,'N')
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*
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* Set up the start point in X if the increment is not unity. This
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* will be ( N - 1 )*INCX too small for descending loops.
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*
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IF (INCX.LE.0) THEN
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KX = 1 - (N-1)*INCX
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ELSE IF (INCX.NE.1) THEN
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KX = 1
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END IF
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*
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* Start the operations. In this version the elements of A are
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* accessed sequentially with one pass through A.
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*
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IF (LSAME(TRANS,'N')) THEN
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*
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* Form x := A*x.
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*
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IF (LSAME(UPLO,'U')) THEN
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IF (INCX.EQ.1) THEN
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DO 20 J = 1,N
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IF (X(J).NE.ZERO) THEN
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TEMP = X(J)
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DO 10 I = 1,J - 1
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X(I) = X(I) + TEMP*A(I,J)
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10 CONTINUE
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IF (NOUNIT) X(J) = X(J)*A(J,J)
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END IF
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20 CONTINUE
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ELSE
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JX = KX
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DO 40 J = 1,N
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IF (X(JX).NE.ZERO) THEN
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TEMP = X(JX)
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IX = KX
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DO 30 I = 1,J - 1
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X(IX) = X(IX) + TEMP*A(I,J)
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IX = IX + INCX
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30 CONTINUE
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IF (NOUNIT) X(JX) = X(JX)*A(J,J)
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END IF
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JX = JX + INCX
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40 CONTINUE
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END IF
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ELSE
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IF (INCX.EQ.1) THEN
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DO 60 J = N,1,-1
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IF (X(J).NE.ZERO) THEN
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TEMP = X(J)
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DO 50 I = N,J + 1,-1
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X(I) = X(I) + TEMP*A(I,J)
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50 CONTINUE
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IF (NOUNIT) X(J) = X(J)*A(J,J)
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END IF
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60 CONTINUE
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ELSE
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KX = KX + (N-1)*INCX
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JX = KX
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DO 80 J = N,1,-1
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IF (X(JX).NE.ZERO) THEN
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TEMP = X(JX)
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IX = KX
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DO 70 I = N,J + 1,-1
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X(IX) = X(IX) + TEMP*A(I,J)
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IX = IX - INCX
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70 CONTINUE
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IF (NOUNIT) X(JX) = X(JX)*A(J,J)
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END IF
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JX = JX - INCX
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80 CONTINUE
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END IF
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END IF
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ELSE
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*
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* Form x := A'*x.
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*
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IF (LSAME(UPLO,'U')) THEN
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IF (INCX.EQ.1) THEN
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DO 100 J = N,1,-1
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TEMP = X(J)
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IF (NOUNIT) TEMP = TEMP*A(J,J)
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DO 90 I = J - 1,1,-1
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TEMP = TEMP + A(I,J)*X(I)
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90 CONTINUE
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X(J) = TEMP
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100 CONTINUE
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ELSE
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JX = KX + (N-1)*INCX
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DO 120 J = N,1,-1
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TEMP = X(JX)
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IX = JX
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IF (NOUNIT) TEMP = TEMP*A(J,J)
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DO 110 I = J - 1,1,-1
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IX = IX - INCX
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TEMP = TEMP + A(I,J)*X(IX)
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110 CONTINUE
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X(JX) = TEMP
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JX = JX - INCX
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120 CONTINUE
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END IF
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ELSE
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IF (INCX.EQ.1) THEN
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DO 140 J = 1,N
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TEMP = X(J)
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IF (NOUNIT) TEMP = TEMP*A(J,J)
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DO 130 I = J + 1,N
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TEMP = TEMP + A(I,J)*X(I)
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130 CONTINUE
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X(J) = TEMP
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140 CONTINUE
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ELSE
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JX = KX
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DO 160 J = 1,N
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TEMP = X(JX)
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IX = JX
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IF (NOUNIT) TEMP = TEMP*A(J,J)
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DO 150 I = J + 1,N
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IX = IX + INCX
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TEMP = TEMP + A(I,J)*X(IX)
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150 CONTINUE
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X(JX) = TEMP
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JX = JX + INCX
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160 CONTINUE
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END IF
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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 DTRMV .
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*
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END
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