NAG Library Routine Document

f06wnf  (zlanhf)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

f06wnf (zlanhf) returns the value of the 1-norm, the -norm, the Frobenius norm, or the maximum absolute value of the elements of a complex Hermitian matrix A stored in Rectangular Full Packed (RFP) format.

2
Specification

Fortran Interface
Function f06wnf ( norm, transr, uplo, n, a, work)
Real (Kind=nag_wp):: f06wnf
Integer, Intent (In):: n
Real (Kind=nag_wp), Intent (Inout):: work(*)
Complex (Kind=nag_wp), Intent (In):: a(n*(n+1)/2)
Character (1), Intent (In):: norm, transr, uplo
C Header Interface
#include nagmk26.h
double  f06wnf_ ( const char *norm, const char *transr, const char *uplo, const Integer *n, const Complex a[], double work[], const Charlen length_norm, const Charlen length_transr, const Charlen length_uplo)
The routine may be called by its LAPACK name zlanhf.

3
Description

Given a complex n by n symmetric matrix, A, f06wnf (zlanhf) calculates one of the values given by
A1=maxji=1naij (the 1-norm of A),
A=maxij= 1naij (the -norm of A),
AF=i=1nj=1naij21/2 (the Frobenius norm of A),   or
maxi,jaij (the maximum absolute element value of A).
A is stored in compact form using the RFP format. The RFP storage format is described in Section 3.3.3 in the F07 Chapter Introduction.

4
References

Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001) Basic Linear Algebra Subprograms Technical (BLAST) Forum Standard University of Tennessee, Knoxville, Tennessee http://www.netlib.org/blas/blast-forum/blas-report.pdf
Gustavson F G, Waśniewski J, Dongarra J J and Langou J (2010) Rectangular full packed format for Cholesky's algorithm: factorization, solution, and inversion ACM Trans. Math. Software 37, 2

5
Arguments

1:     norm – Character(1)Input
On entry: specifies the value to be returned.
norm='1' or 'O'
The 1-norm.
norm='I'
The -norm.
norm='F' or 'E'
The Frobenius (or Euclidean) norm.
norm='M'
The value maxi,jaij (not a norm).
Constraint: norm='1', 'O', 'I', 'F', 'E' or 'M'.
2:     transr – Character(1)Input
On entry: specifies whether the normal RFP representation of A or its conjugate transpose is stored.
transr='N'
The matrix A is stored in normal RFP format.
transr='C'
The conjugate transpose of the RFP representation of the matrix A is stored.
Constraint: transr='N' or 'C'.
3:     uplo – Character(1)Input
On entry: specifies whether the upper or lower triangular part of A is stored.
uplo='U'
The upper triangular part of A is stored.
uplo='L'
The lower triangular part of A is stored.
Constraint: uplo='U' or 'L'.
4:     n – IntegerInput
On entry: n, the order of the matrix A.
When n=0, f06wnf (zlanhf) returns zero.
Constraint: n0.
5:     an×n+1/2 – Complex (Kind=nag_wp) arrayInput
On entry: the upper or lower triangular part (as specified by uplo) of the n by n Hermitian matrix A, in either normal or transposed RFP format (as specified by transr). The storage format is described in detail in Section 3.3.3 in the F07 Chapter Introduction.
6:     work* – Real (Kind=nag_wp) arrayWorkspace
Note: the dimension of the array work must be at least max1,n  if norm='1', 'O' or 'I', and at least 1 otherwise.

6
Error Indicators and Warnings

None.

7
Accuracy

The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)).

8
Parallelism and Performance

f06wnf (zlanhf) is not threaded in any implementation.

9
Further Comments

None.

10
Example

This example reads in the lower triangular part of a symmetric matrix, converts this to RFP format, then calculates the norm of the matrix for each of the available norm types.

10.1
Program Text

Program Text (f06wnfe.f90)

10.2
Program Data

Program Data (f06wnfe.d)

10.3
Program Results

Program Results (f06wnfe.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017