numeric-linalg

Educational material on the SciPy implementation of numerical linear algebra algorithms

Name	Size	Mode
..
lapack/SRC/dlantb.f	11523B	-rw-r--r--

*> \brief \b DLANTB 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 band matrix.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download DLANTB + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlantb.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlantb.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlantb.f">
*> [TXT]</a>
*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       DOUBLE PRECISION FUNCTION DLANTB( NORM, UPLO, DIAG, N, K, AB,
*                        LDAB, WORK )
*
*       .. Scalar Arguments ..
*       CHARACTER          DIAG, NORM, UPLO
*       INTEGER            K, LDAB, N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION   AB( LDAB, * ), WORK( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> DLANTB  returns the value of the one norm,  or the Frobenius norm, or
*> the  infinity norm,  or the element of  largest absolute value  of an
*> n by n triangular band matrix A,  with ( k + 1 ) diagonals.
*> \endverbatim
*>
*> \return DLANTB
*> \verbatim
*>
*>    DLANTB = ( 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 DLANTB 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, DLANTB is
*>          set to zero.
*> \endverbatim
*>
*> \param[in] K
*> \verbatim
*>          K is INTEGER
*>          The number of super-diagonals of the matrix A if UPLO = 'U',
*>          or the number of sub-diagonals of the matrix A if UPLO = 'L'.
*>          K >= 0.
*> \endverbatim
*>
*> \param[in] AB
*> \verbatim
*>          AB is DOUBLE PRECISION array, dimension (LDAB,N)
*>          The upper or lower triangular band matrix A, stored in the
*>          first k+1 rows of AB.  The j-th column of A is stored
*>          in the j-th column of the array AB as follows:
*>          if UPLO = 'U', AB(k+1+i-j,j) = A(i,j) for max(1,j-k)<=i<=j;
*>          if UPLO = 'L', AB(1+i-j,j)   = A(i,j) for j<=i<=min(n,j+k).
*>          Note that when DIAG = 'U', the elements of the array AB
*>          corresponding to the diagonal elements of the matrix A are
*>          not referenced, but are assumed to be one.
*> \endverbatim
*>
*> \param[in] LDAB
*> \verbatim
*>          LDAB is INTEGER
*>          The leading dimension of the array AB.  LDAB >= K+1.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is DOUBLE PRECISION 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.
*
*> \ingroup lantb
*
*  =====================================================================
      DOUBLE PRECISION FUNCTION DLANTB( NORM, UPLO, DIAG, N, K, AB,
     $                 LDAB, WORK )
*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          DIAG, NORM, UPLO
      INTEGER            K, LDAB, N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   AB( LDAB, * ), WORK( * )
*     ..
*
* =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ONE, ZERO
      PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            UDIAG
      INTEGER            I, J, L
      DOUBLE PRECISION   SCALE, SUM, VALUE
*     ..
*     .. External Subroutines ..
      EXTERNAL           DLASSQ
*     ..
*     .. External Functions ..
      LOGICAL            LSAME, DISNAN
      EXTERNAL           LSAME, DISNAN
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS, MAX, MIN, SQRT
*     ..
*     .. Executable Statements ..
*
      IF( N.EQ.0 ) THEN
         VALUE = ZERO
      ELSE IF( LSAME( NORM, 'M' ) ) THEN
*
*        Find max(abs(A(i,j))).
*
         IF( LSAME( DIAG, 'U' ) ) THEN
            VALUE = ONE
            IF( LSAME( UPLO, 'U' ) ) THEN
               DO 20 J = 1, N
                  DO 10 I = MAX( K+2-J, 1 ), K
                     SUM = ABS( AB( I, J ) )
                     IF( VALUE .LT. SUM .OR.
     $                   DISNAN( SUM ) ) VALUE = SUM
   10             CONTINUE
   20          CONTINUE
            ELSE
               DO 40 J = 1, N
                  DO 30 I = 2, MIN( N+1-J, K+1 )
                     SUM = ABS( AB( I, J ) )
                     IF( VALUE .LT. SUM .OR.
     $                   DISNAN( SUM ) ) VALUE = SUM
   30             CONTINUE
   40          CONTINUE
            END IF
         ELSE
            VALUE = ZERO
            IF( LSAME( UPLO, 'U' ) ) THEN
               DO 60 J = 1, N
                  DO 50 I = MAX( K+2-J, 1 ), K + 1
                     SUM = ABS( AB( I, J ) )
                     IF( VALUE .LT. SUM .OR.
     $                   DISNAN( SUM ) ) VALUE = SUM
   50             CONTINUE
   60          CONTINUE
            ELSE
               DO 80 J = 1, N
                  DO 70 I = 1, MIN( N+1-J, K+1 )
                     SUM = ABS( AB( I, J ) )
                     IF( VALUE .LT. SUM .OR.
     $                   DISNAN( SUM ) ) VALUE = SUM
   70             CONTINUE
   80          CONTINUE
            END IF
         END IF
      ELSE IF( ( LSAME( NORM, 'O' ) ) .OR. ( NORM.EQ.'1' ) ) THEN
*
*        Find norm1(A).
*
         VALUE = ZERO
         UDIAG = LSAME( DIAG, 'U' )
         IF( LSAME( UPLO, 'U' ) ) THEN
            DO 110 J = 1, N
               IF( UDIAG ) THEN
                  SUM = ONE
                  DO 90 I = MAX( K+2-J, 1 ), K
                     SUM = SUM + ABS( AB( I, J ) )
   90             CONTINUE
               ELSE
                  SUM = ZERO
                  DO 100 I = MAX( K+2-J, 1 ), K + 1
                     SUM = SUM + ABS( AB( I, J ) )
  100             CONTINUE
               END IF
               IF( VALUE .LT. SUM .OR. DISNAN( SUM ) ) VALUE = SUM
  110       CONTINUE
         ELSE
            DO 140 J = 1, N
               IF( UDIAG ) THEN
                  SUM = ONE
                  DO 120 I = 2, MIN( N+1-J, K+1 )
                     SUM = SUM + ABS( AB( I, J ) )
  120             CONTINUE
               ELSE
                  SUM = ZERO
                  DO 130 I = 1, MIN( N+1-J, K+1 )
                     SUM = SUM + ABS( AB( I, J ) )
  130             CONTINUE
               END IF
               IF( VALUE .LT. SUM .OR. DISNAN( SUM ) ) VALUE = SUM
  140       CONTINUE
         END IF
      ELSE IF( LSAME( NORM, 'I' ) ) THEN
*
*        Find normI(A).
*
         VALUE = ZERO
         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
                  L = K + 1 - J
                  DO 160 I = MAX( 1, J-K ), J - 1
                     WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) )
  160             CONTINUE
  170          CONTINUE
            ELSE
               DO 180 I = 1, N
                  WORK( I ) = ZERO
  180          CONTINUE
               DO 200 J = 1, N
                  L = K + 1 - J
                  DO 190 I = MAX( 1, J-K ), J
                     WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) )
  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
                  L = 1 - J
                  DO 220 I = J + 1, MIN( N, J+K )
                     WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) )
  220             CONTINUE
  230          CONTINUE
            ELSE
               DO 240 I = 1, N
                  WORK( I ) = ZERO
  240          CONTINUE
               DO 260 J = 1, N
                  L = 1 - J
                  DO 250 I = J, MIN( N, J+K )
                     WORK( I ) = WORK( I ) + ABS( AB( L+I, J ) )
  250             CONTINUE
  260          CONTINUE
            END IF
         END IF
         DO 270 I = 1, N
            SUM = WORK( I )
            IF( VALUE .LT. SUM .OR. DISNAN( SUM ) ) VALUE = SUM
  270    CONTINUE
      ELSE IF( ( LSAME( NORM, 'F' ) ) .OR.
     $         ( LSAME( NORM, 'E' ) ) ) THEN
*
*        Find normF(A).
*
         IF( LSAME( UPLO, 'U' ) ) THEN
            IF( LSAME( DIAG, 'U' ) ) THEN
               SCALE = ONE
               SUM = N
               IF( K.GT.0 ) THEN
                  DO 280 J = 2, N
                     CALL DLASSQ( MIN( J-1, K ),
     $                            AB( MAX( K+2-J, 1 ), J ), 1, SCALE,
     $                            SUM )
  280             CONTINUE
               END IF
            ELSE
               SCALE = ZERO
               SUM = ONE
               DO 290 J = 1, N
                  CALL DLASSQ( MIN( J, K+1 ), AB( MAX( K+2-J, 1 ),
     $                         J ),
     $                         1, SCALE, SUM )
  290          CONTINUE
            END IF
         ELSE
            IF( LSAME( DIAG, 'U' ) ) THEN
               SCALE = ONE
               SUM = N
               IF( K.GT.0 ) THEN
                  DO 300 J = 1, N - 1
                     CALL DLASSQ( MIN( N-J, K ), AB( 2, J ), 1,
     $                            SCALE,
     $                            SUM )
  300             CONTINUE
               END IF
            ELSE
               SCALE = ZERO
               SUM = ONE
               DO 310 J = 1, N
                  CALL DLASSQ( MIN( N-J+1, K+1 ), AB( 1, J ), 1,
     $                         SCALE,
     $                         SUM )
  310          CONTINUE
            END IF
         END IF
         VALUE = SCALE*SQRT( SUM )
      END IF
*
      DLANTB = VALUE
      RETURN
*
*     End of DLANTB
*
      END