199 lines
5.9 KiB
Fortran
199 lines
5.9 KiB
Fortran
SUBROUTINE DSPRF ( UPLO, N, ALPHA, X, INCX, AP )
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* .. Scalar Arguments ..
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DOUBLE PRECISION ALPHA
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INTEGER INCX, N
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CHARACTER*1 UPLO
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* .. Array Arguments ..
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DOUBLE PRECISION AP( * ), 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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* DSPR performs the symmetric rank 1 operation
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*
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* A := alpha*x*x' + A,
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*
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* where alpha is a real scalar, x is an n element vector and A is an
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* n by n symmetric matrix, supplied in packed form.
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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 matrix A is supplied in the packed
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* array AP as follows:
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*
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* UPLO = 'U' or 'u' The upper triangular part of A is
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* supplied in AP.
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*
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* UPLO = 'L' or 'l' The lower triangular part of A is
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* supplied in AP.
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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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* ALPHA - DOUBLE PRECISION.
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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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* 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.
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* Unchanged on exit.
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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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* AP - DOUBLE PRECISION array of DIMENSION at least
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* ( ( n*( n + 1 ) )/2 ).
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* Before entry with UPLO = 'U' or 'u', the array AP must
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* contain the upper triangular part of the symmetric matrix
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* packed sequentially, column by column, so that AP( 1 )
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* contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )
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* and a( 2, 2 ) respectively, and so on. On exit, the array
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* AP is overwritten by the upper triangular part of the
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* updated matrix.
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* Before entry with UPLO = 'L' or 'l', the array AP must
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* contain the lower triangular part of the symmetric matrix
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* packed sequentially, column by column, so that AP( 1 )
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* contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )
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* and a( 3, 1 ) respectively, and so on. On exit, the array
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* AP is overwritten by the lower triangular part of the
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* updated matrix.
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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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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D+0 )
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* .. Local Scalars ..
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DOUBLE PRECISION TEMP
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INTEGER I, INFO, IX, J, JX, K, KK, KX
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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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* ..
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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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INFO = 0
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IF ( .NOT.LSAME( UPLO, 'U' ).AND.
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$ .NOT.LSAME( UPLO, 'L' ) )THEN
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INFO = 1
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ELSE IF( N.LT.0 )THEN
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INFO = 2
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ELSE IF( INCX.EQ.0 )THEN
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INFO = 5
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END IF
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IF( INFO.NE.0 )THEN
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CALL XERBLA( 'DSPR ', 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.( ALPHA.EQ.ZERO ) )
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$ RETURN
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*
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* Set the start point in X if the increment is not unity.
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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 the array AP
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* are accessed sequentially with one pass through AP.
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*
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KK = 1
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IF( LSAME( UPLO, 'U' ) )THEN
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*
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* Form A when upper triangle is stored in AP.
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*
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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 = ALPHA*X( J )
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K = KK
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DO 10, I = 1, J
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AP( K ) = AP( K ) + X( I )*TEMP
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K = K + 1
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10 CONTINUE
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END IF
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KK = KK + J
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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 = ALPHA*X( JX )
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IX = KX
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DO 30, K = KK, KK + J - 1
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AP( K ) = AP( K ) + X( IX )*TEMP
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IX = IX + INCX
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30 CONTINUE
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END IF
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JX = JX + INCX
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KK = KK + J
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40 CONTINUE
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END IF
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ELSE
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*
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* Form A when lower triangle is stored in AP.
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*
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IF( INCX.EQ.1 )THEN
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DO 60, J = 1, N
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IF( X( J ).NE.ZERO )THEN
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TEMP = ALPHA*X( J )
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K = KK
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DO 50, I = J, N
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AP( K ) = AP( K ) + X( I )*TEMP
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K = K + 1
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50 CONTINUE
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END IF
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KK = KK + N - J + 1
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60 CONTINUE
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ELSE
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JX = KX
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DO 80, J = 1, N
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IF( X( JX ).NE.ZERO )THEN
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TEMP = ALPHA*X( JX )
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IX = JX
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DO 70, K = KK, KK + N - J
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AP( K ) = AP( K ) + X( IX )*TEMP
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IX = IX + INCX
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70 CONTINUE
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END IF
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JX = JX + INCX
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KK = KK + N - J + 1
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80 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 DSPR .
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*
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END
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