


SLANGT(3f)    LAPACK auxiliary routine (version 3.1)   SLANGT(3f)


NAME
       SLANGT  -  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
       REAL FUNCTION SLANGT( NORM, N, DL, D, DU )

           CHARACTER NORM

           INTEGER   N

           REAL      D( * ), DL( * ), DU( * )

PURPOSE
       SLANGT   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
       SLANGT returns the value

          SLANGT = ( 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.


ARGUMENTS
       NORM    (input) CHARACTER*1
               Specifies  the  value  to  be  returned  in SLANGT as described
               above.

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

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

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





 LAPACK auxiliary routine November 2006                         1





SLANGT(3f)    LAPACK auxiliary routine (version 3.1)   SLANGT(3f)


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























































 LAPACK auxiliary routine November 2006                         2


