Previous: slanst Up: ../lapack-s.html Next: slantb

slansy

 NAME
      SLANSY - return the value of the one norm, or the Frobenius
      norm, or the infinity norm, or the element of largest abso-
      lute value of a real symmetric matrix A

 SYNOPSIS
      REAL FUNCTION SLANSY( NORM, UPLO, N, A, LDA, WORK )

          CHARACTER NORM, UPLO

          INTEGER   LDA, N

          REAL      A( LDA, * ), WORK( * )

 PURPOSE
      SLANSY  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 symmetric matrix A.

 DESCRIPTION
      SLANSY returns the value

         SLANSY = ( 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 SLANSY as
              described above.

      UPLO    (input) CHARACTER*1
              Specifies whether the upper or lower triangular part
              of the symmetric matrix A is to be referenced.  =
              'U':  Upper triangular part of A is referenced
              = 'L':  Lower triangular part of A is referenced

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

      A       (input) REAL array, dimension (LDA,N)
              The symmetric matrix A.  If UPLO = 'U', the leading
              n by n upper triangular part of A contains the upper
              triangular part of the matrix A, and the strictly
              lower triangular part of A is not referenced.  If
              UPLO = 'L', the leading n by n lower triangular part
              of A contains the lower triangular part of the
              matrix A, and the strictly upper triangular part of
              A is not referenced.

      LDA     (input) INTEGER
              The leading dimension of the array A.  LDA >=
              max(N,1).

      WORK    (workspace) REAL array, dimension (LWORK),
              where LWORK >= N when NORM = 'I' or '1' or 'O'; oth-
              erwise, WORK is not referenced.