dlangt(3S)

NAME
     DLANGT - return the value of the one norm, or the Frobenius norm, or the
     infinity norm, or the element of largest absolute value of a real
     tridiagonal matrix A

SYNOPSIS
     DOUBLE PRECISION FUNCTION DLANGT( NORM, N, DL, D, DU )

         CHARACTER    NORM

         INTEGER      N

         DOUBLE       PRECISION D( * ), DL( * ), DU( * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     DLANGT returns the value of the one norm, or the Frobenius norm, or the
     infinity norm, or the element of largest absolute value of a real
     tridiagonal matrix A.

DESCRIPTION
     DLANGT returns the value

        DLANGT = ( 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  matrix norm.
ARGUMENTS
     NORM    (input) CHARACTER*1
             Specifies the value to be returned in DLANGT as described above.

     N       (input) INTEGER
             The order of the matrix A.  N >= 0.  When N = 0, DLANGT is set to
             zero.

     DL      (input) DOUBLE PRECISION array, dimension (N-1)
             The (n-1) sub-diagonal elements of A.

     D       (input) DOUBLE PRECISION array, dimension (N)
             The diagonal elements of A.

     DU      (input) DOUBLE PRECISION array, dimension (N-1)
             The (n-1) super-diagonal elements of A.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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