OpenBLAS/lapack-netlib/SRC/slantp.f

*> \brief \b SLANTP returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a triangular matrix supplied in packed form.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slantp.f">
*> [TXT]</a>
*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       REAL             FUNCTION SLANTP( NORM, UPLO, DIAG, N, AP, WORK )
*
*       .. Scalar Arguments ..
*       CHARACTER          DIAG, NORM, UPLO
*       INTEGER            N
*       ..
*       .. Array Arguments ..
*       REAL               AP( * ), WORK( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SLANTP  returns the value of the one norm,  or the Frobenius norm, or
*> the  infinity norm,  or the  element of  largest absolute value  of a
*> triangular matrix A, supplied in packed form.
*> \endverbatim
*>
*> \return SLANTP
*> \verbatim
*>
*>    SLANTP = ( max(abs(A(i,j))), NORM = 'M' or 'm'
*>             (
*>             ( norm1(A),         NORM = '1', 'O' or 'o'
*>             (
*>             ( normI(A),         NORM = 'I' or 'i'
*>             (
*>             ( normF(A),         NORM = 'F', 'f', 'E' or 'e'
*>
*> where  norm1  denotes the  one norm of a matrix (maximum column sum),
*> normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
*> normF  denotes the  Frobenius norm of a matrix (square root of sum of
*> squares).  Note that  max(abs(A(i,j)))  is not a consistent matrix norm.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] NORM
*> \verbatim
*>          NORM is CHARACTER*1
*>          Specifies the value to be returned in SLANTP as described
*>          above.
*> \endverbatim
*>
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          Specifies whether the matrix A is upper or lower triangular.
*>          = 'U':  Upper triangular
*>          = 'L':  Lower triangular
*> \endverbatim
*>
*> \param[in] DIAG
*> \verbatim
*>          DIAG is CHARACTER*1
*>          Specifies whether or not the matrix A is unit triangular.
*>          = 'N':  Non-unit triangular
*>          = 'U':  Unit triangular
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The order of the matrix A.  N >= 0.  When N = 0, SLANTP is
*>          set to zero.
*> \endverbatim
*>
*> \param[in] AP
*> \verbatim
*>          AP is REAL array, dimension (N*(N+1)/2)
*>          The upper or lower triangular matrix A, packed columnwise in
*>          a linear array.  The j-th column of A is stored in the array
*>          AP as follows:
*>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
*>          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
*>          Note that when DIAG = 'U', the elements of the array AP
*>          corresponding to the diagonal elements of the matrix A are
*>          not referenced, but are assumed to be one.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is REAL array, dimension (MAX(1,LWORK)),
*>          where LWORK >= N when NORM = 'I'; otherwise, WORK is not
*>          referenced.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup realOTHERauxiliary
*
*  =====================================================================
      REAL             FUNCTION SLANTP( NORM, UPLO, DIAG, N, AP, WORK )
*
*  -- LAPACK auxiliary routine (version 3.7.0) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     December 2016
*
      IMPLICIT NONE
*     .. Scalar Arguments ..
      CHARACTER          DIAG, NORM, UPLO
      INTEGER            N
*     ..
*     .. Array Arguments ..
      REAL               AP( * ), WORK( * )
*     ..
*
* =====================================================================
*
*     .. Parameters ..
      REAL               ONE, ZERO
      PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            UDIAG
      INTEGER            I, J, K
      REAL               SUM, VALUE
*     ..
*     .. Local Arrays ..
      REAL               SSQ( 2 ), COLSSQ( 2 )
*     ..
*     .. External Functions ..
      LOGICAL            LSAME, SISNAN
      EXTERNAL           LSAME, SISNAN
*     ..
*     .. External Subroutines ..
      EXTERNAL           SLASSQ, SCOMBSSQ
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS, SQRT
*     ..
*     .. Executable Statements ..
*
      IF( N.EQ.0 ) THEN
         VALUE = ZERO
      ELSE IF( LSAME( NORM, 'M' ) ) THEN
*
*        Find max(abs(A(i,j))).
*
         K = 1
         IF( LSAME( DIAG, 'U' ) ) THEN
            VALUE = ONE
            IF( LSAME( UPLO, 'U' ) ) THEN
               DO 20 J = 1, N
                  DO 10 I = K, K + J - 2
                     SUM = ABS( AP( I ) )
                     IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
   10             CONTINUE
                  K = K + J
   20          CONTINUE
            ELSE
               DO 40 J = 1, N
                  DO 30 I = K + 1, K + N - J
                     SUM = ABS( AP( I ) )
                     IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
   30             CONTINUE
                  K = K + N - J + 1
   40          CONTINUE
            END IF
         ELSE
            VALUE = ZERO
            IF( LSAME( UPLO, 'U' ) ) THEN
               DO 60 J = 1, N
                  DO 50 I = K, K + J - 1
                     SUM = ABS( AP( I ) )
                     IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
   50             CONTINUE
                  K = K + J
   60          CONTINUE
            ELSE
               DO 80 J = 1, N
                  DO 70 I = K, K + N - J
                     SUM = ABS( AP( I ) )
                     IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
   70             CONTINUE
                  K = K + N - J + 1
   80          CONTINUE
            END IF
         END IF
      ELSE IF( ( LSAME( NORM, 'O' ) ) .OR. ( NORM.EQ.'1' ) ) THEN
*
*        Find norm1(A).
*
         VALUE = ZERO
         K = 1
         UDIAG = LSAME( DIAG, 'U' )
         IF( LSAME( UPLO, 'U' ) ) THEN
            DO 110 J = 1, N
               IF( UDIAG ) THEN
                  SUM = ONE
                  DO 90 I = K, K + J - 2
                     SUM = SUM + ABS( AP( I ) )
   90             CONTINUE
               ELSE
                  SUM = ZERO
                  DO 100 I = K, K + J - 1
                     SUM = SUM + ABS( AP( I ) )
  100             CONTINUE
               END IF
               K = K + J
               IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
  110       CONTINUE
         ELSE
            DO 140 J = 1, N
               IF( UDIAG ) THEN
                  SUM = ONE
                  DO 120 I = K + 1, K + N - J
                     SUM = SUM + ABS( AP( I ) )
  120             CONTINUE
               ELSE
                  SUM = ZERO
                  DO 130 I = K, K + N - J
                     SUM = SUM + ABS( AP( I ) )
  130             CONTINUE
               END IF
               K = K + N - J + 1
               IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
  140       CONTINUE
         END IF
      ELSE IF( LSAME( NORM, 'I' ) ) THEN
*
*        Find normI(A).
*
         K = 1
         IF( LSAME( UPLO, 'U' ) ) THEN
            IF( LSAME( DIAG, 'U' ) ) THEN
               DO 150 I = 1, N
                  WORK( I ) = ONE
  150          CONTINUE
               DO 170 J = 1, N
                  DO 160 I = 1, J - 1
                     WORK( I ) = WORK( I ) + ABS( AP( K ) )
                     K = K + 1
  160             CONTINUE
                  K = K + 1
  170          CONTINUE
            ELSE
               DO 180 I = 1, N
                  WORK( I ) = ZERO
  180          CONTINUE
               DO 200 J = 1, N
                  DO 190 I = 1, J
                     WORK( I ) = WORK( I ) + ABS( AP( K ) )
                     K = K + 1
  190             CONTINUE
  200          CONTINUE
            END IF
         ELSE
            IF( LSAME( DIAG, 'U' ) ) THEN
               DO 210 I = 1, N
                  WORK( I ) = ONE
  210          CONTINUE
               DO 230 J = 1, N
                  K = K + 1
                  DO 220 I = J + 1, N
                     WORK( I ) = WORK( I ) + ABS( AP( K ) )
                     K = K + 1
  220             CONTINUE
  230          CONTINUE
            ELSE
               DO 240 I = 1, N
                  WORK( I ) = ZERO
  240          CONTINUE
               DO 260 J = 1, N
                  DO 250 I = J, N
                     WORK( I ) = WORK( I ) + ABS( AP( K ) )
                     K = K + 1
  250             CONTINUE
  260          CONTINUE
            END IF
         END IF
         VALUE = ZERO
         DO 270 I = 1, N
            SUM = WORK( I )
            IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
  270    CONTINUE
      ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
*
*        Find normF(A).
*        SSQ(1) is scale
*        SSQ(2) is sum-of-squares
*        For better accuracy, sum each column separately.
*
         IF( LSAME( UPLO, 'U' ) ) THEN
            IF( LSAME( DIAG, 'U' ) ) THEN
               SSQ( 1 ) = ONE
               SSQ( 2 ) = N
               K = 2
               DO 280 J = 2, N
                  COLSSQ( 1 ) = ZERO
                  COLSSQ( 2 ) = ONE
                  CALL SLASSQ( J-1, AP( K ), 1,
     $                         COLSSQ( 1 ), COLSSQ( 2 ) )
                  CALL SCOMBSSQ( SSQ, COLSSQ )
                  K = K + J
  280          CONTINUE
            ELSE
               SSQ( 1 ) = ZERO
               SSQ( 2 ) = ONE
               K = 1
               DO 290 J = 1, N
                  COLSSQ( 1 ) = ZERO
                  COLSSQ( 2 ) = ONE
                  CALL SLASSQ( J, AP( K ), 1,
     $                         COLSSQ( 1 ), COLSSQ( 2 ) )
                  CALL SCOMBSSQ( SSQ, COLSSQ )
                  K = K + J
  290          CONTINUE
            END IF
         ELSE
            IF( LSAME( DIAG, 'U' ) ) THEN
               SSQ( 1 ) = ONE
               SSQ( 2 ) = N
               K = 2
               DO 300 J = 1, N - 1
                  COLSSQ( 1 ) = ZERO
                  COLSSQ( 2 ) = ONE
                  CALL SLASSQ( N-J, AP( K ), 1,
     $                         COLSSQ( 1 ), COLSSQ( 2 ) )
                  CALL SCOMBSSQ( SSQ, COLSSQ )
                  K = K + N - J + 1
  300          CONTINUE
            ELSE
               SSQ( 1 ) = ZERO
               SSQ( 2 ) = ONE
               K = 1
               DO 310 J = 1, N
                  COLSSQ( 1 ) = ZERO
                  COLSSQ( 2 ) = ONE
                  CALL SLASSQ( N-J+1, AP( K ), 1,
     $                         COLSSQ( 1 ), COLSSQ( 2 ) )
                  CALL SCOMBSSQ( SSQ, COLSSQ )
                  K = K + N - J + 1
  310          CONTINUE
            END IF
         END IF
         VALUE = SSQ( 1 )*SQRT( SSQ( 2 ) )
      END IF
*
      SLANTP = VALUE
      RETURN
*
*     End of SLANTP
*
      END