Previous: slamch Up: ../lapack-s.html Next: slange

slangb

 NAME
      SLANGB - return the value of the one norm, or the Frobenius
      norm, or the infinity norm, or the element of largest abso-
      lute value of an n by n band matrix A, with kl sub-diagonals
      and ku super-diagonals

 SYNOPSIS
      REAL FUNCTION SLANGB( NORM, N, KL, KU, AB, LDAB, WORK )

          CHARACTER NORM

          INTEGER   KL, KU, LDAB, N

          REAL      AB( LDAB, * ), WORK( * )

 PURPOSE
      SLANGB  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 band matrix  A,  with kl sub-
      diagonals and ku super-diagonals.

 DESCRIPTION
      SLANGB returns the value

         SLANGB = ( 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 SLANGB as
              described above.

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

      KL      (input) INTEGER
              The number of sub-diagonals of the matrix A.  KL >=
              0.

      KU      (input) INTEGER
              The number of super-diagonals of the matrix A.  KU
              >= 0.

      AB      (input) REAL array, dimension (LDAB,N)
              The band matrix A, stored in rows 1 to KL+KU+1.  The
              j-th column of A is stored in the j-th column of the
              array AB as follows: AB(ku+1+i-j,j) = A(i,j) for
              max(1,j-ku)<=i<=min(n,j+kl).

      LDAB    (input) INTEGER
              The leading dimension of the array AB.  LDAB >=
              KL+KU+1.

      WORK    (workspace) REAL array, dimension (LWORK),
              where LWORK >= N when NORM = 'I'; otherwise, WORK is
              not referenced.