version 1.5, 2010/08/13 21:03:41
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version 1.18, 2023/08/07 08:38:44
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*> \brief \b IDAMAX |
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* |
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* =========== DOCUMENTATION =========== |
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* |
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* Online html documentation available at |
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* http://www.netlib.org/lapack/explore-html/ |
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* |
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* Definition: |
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* =========== |
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* |
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* INTEGER FUNCTION IDAMAX(N,DX,INCX) |
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* |
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* .. Scalar Arguments .. |
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* INTEGER INCX,N |
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* .. |
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* .. Array Arguments .. |
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* DOUBLE PRECISION DX(*) |
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* .. |
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* |
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* |
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*> \par Purpose: |
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* ============= |
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*> |
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*> \verbatim |
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*> |
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*> IDAMAX finds the index of the first element having maximum absolute value. |
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*> \endverbatim |
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* |
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* Arguments: |
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* ========== |
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* |
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*> \param[in] N |
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*> \verbatim |
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*> N is INTEGER |
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*> number of elements in input vector(s) |
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*> \endverbatim |
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*> |
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*> \param[in] DX |
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*> \verbatim |
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*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) ) |
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*> \endverbatim |
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*> |
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*> \param[in] INCX |
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*> \verbatim |
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*> INCX is INTEGER |
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*> storage spacing between elements of DX |
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*> \endverbatim |
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* |
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* Authors: |
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* ======== |
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* |
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*> \author Univ. of Tennessee |
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*> \author Univ. of California Berkeley |
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*> \author Univ. of Colorado Denver |
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*> \author NAG Ltd. |
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* |
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*> \ingroup aux_blas |
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* |
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*> \par Further Details: |
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* ===================== |
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*> |
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*> \verbatim |
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*> |
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*> jack dongarra, linpack, 3/11/78. |
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*> modified 3/93 to return if incx .le. 0. |
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*> modified 12/3/93, array(1) declarations changed to array(*) |
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*> \endverbatim |
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*> |
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* ===================================================================== |
INTEGER FUNCTION IDAMAX(N,DX,INCX) |
INTEGER FUNCTION IDAMAX(N,DX,INCX) |
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* |
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* -- Reference BLAS level1 routine -- |
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* -- Reference BLAS is a software package provided by Univ. of Tennessee, -- |
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
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* |
* .. Scalar Arguments .. |
* .. Scalar Arguments .. |
INTEGER INCX,N |
INTEGER INCX,N |
* .. |
* .. |
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DOUBLE PRECISION DX(*) |
DOUBLE PRECISION DX(*) |
* .. |
* .. |
* |
* |
* Purpose |
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* ======= |
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* |
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* IDAMAX finds the index of element having max. absolute value. |
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* |
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* Further Details |
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* =============== |
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* |
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* jack dongarra, linpack, 3/11/78. |
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* modified 3/93 to return if incx .le. 0. |
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* modified 12/3/93, array(1) declarations changed to array(*) |
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* |
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* ===================================================================== |
* ===================================================================== |
* |
* |
* .. Local Scalars .. |
* .. Local Scalars .. |
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IF (N.LT.1 .OR. INCX.LE.0) RETURN |
IF (N.LT.1 .OR. INCX.LE.0) RETURN |
IDAMAX = 1 |
IDAMAX = 1 |
IF (N.EQ.1) RETURN |
IF (N.EQ.1) RETURN |
IF (INCX.EQ.1) GO TO 20 |
IF (INCX.EQ.1) THEN |
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* |
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* code for increment equal to 1 |
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* |
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DMAX = DABS(DX(1)) |
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DO I = 2,N |
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IF (DABS(DX(I)).GT.DMAX) THEN |
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IDAMAX = I |
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DMAX = DABS(DX(I)) |
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END IF |
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END DO |
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ELSE |
* |
* |
* code for increment not equal to 1 |
* code for increment not equal to 1 |
* |
* |
IX = 1 |
IX = 1 |
DMAX = DABS(DX(1)) |
DMAX = DABS(DX(1)) |
IX = IX + INCX |
IX = IX + INCX |
DO 10 I = 2,N |
DO I = 2,N |
IF (DABS(DX(IX)).LE.DMAX) GO TO 5 |
IF (DABS(DX(IX)).GT.DMAX) THEN |
IDAMAX = I |
IDAMAX = I |
DMAX = DABS(DX(IX)) |
DMAX = DABS(DX(IX)) |
5 IX = IX + INCX |
END IF |
10 CONTINUE |
IX = IX + INCX |
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END DO |
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END IF |
RETURN |
RETURN |
* |
* |
* code for increment equal to 1 |
* End of IDAMAX |
* |
* |
20 DMAX = DABS(DX(1)) |
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DO 30 I = 2,N |
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IF (DABS(DX(I)).LE.DMAX) GO TO 30 |
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IDAMAX = I |
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DMAX = DABS(DX(I)) |
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30 CONTINUE |
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RETURN |
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END |
END |