NAG Library Function Document

nag_dsp_norm (f16rdc)

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1
Purpose

nag_dsp_norm (f16rdc) calculates the value of the 1-norm, the -norm, the Frobenius norm or the maximum absolute value of the elements of a real n by n symmetric matrix, stored in packed form.

2
Specification

#include <nag.h>
#include <nagf16.h>
void  nag_dsp_norm (Nag_OrderType order, Nag_NormType norm, Nag_UploType uplo, Integer n, const double ap[], double *r, NagError *fail)

3
Description

Given a real n by n symmetric matrix, A, in packed storage, nag_dsp_norm (f16rdc) calculates one of the values given by
A1=maxji=1naij,  
A=maxij= 1naij,  
AF=i=1nj=1n aij21/2  
or
maxi,jaij.  
Note that, since A is symmetric, A1=A.

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

5
Arguments

1:     order Nag_OrderTypeInput
On entry: the order argument specifies the two-dimensional storage scheme being used, i.e., row-major ordering or column-major ordering. C language defined storage is specified by order=Nag_RowMajor. See Section 3.3.1.3 in How to Use the NAG Library and its Documentation for a more detailed explanation of the use of this argument.
Constraint: order=Nag_RowMajor or Nag_ColMajor.
2:     norm Nag_NormTypeInput
On entry: specifies the value to be returned.
norm=Nag_OneNorm
The 1-norm.
norm=Nag_InfNorm
The -norm.
norm=Nag_FrobeniusNorm
The Frobenius (or Euclidean) norm.
norm=Nag_MaxNorm
The value maxi,jaij (not a norm).
Constraint: norm=Nag_OneNorm, Nag_InfNorm, Nag_FrobeniusNorm or Nag_MaxNorm.
3:     uplo Nag_UploTypeInput
On entry: specifies whether the upper or lower triangular part of A is stored.
uplo=Nag_Upper
The upper triangular part of A is stored.
uplo=Nag_Lower
The lower triangular part of A is stored.
Constraint: uplo=Nag_Upper or Nag_Lower.
4:     n IntegerInput
On entry: n, the order of the matrix A.
If n=0, n is set to zero.
Constraint: n0.
5:     ap[dim] const doubleInput
Note: the dimension, dim, of the array ap must be at least max1, n × n+1 / 2 .
On entry: the n by n symmetric matrix A, packed by rows or columns.
The storage of elements Aij depends on the order and uplo arguments as follows:
  • if order=Nag_ColMajor and uplo=Nag_Upper,
              Aij is stored in ap[j-1×j/2+i-1], for ij;
  • if order=Nag_ColMajor and uplo=Nag_Lower,
              Aij is stored in ap[2n-j×j-1/2+i-1], for ij;
  • if order=Nag_RowMajor and uplo=Nag_Upper,
              Aij is stored in ap[2n-i×i-1/2+j-1], for ij;
  • if order=Nag_RowMajor and uplo=Nag_Lower,
              Aij is stored in ap[i-1×i/2+j-1], for ij.
6:     r double *Output
On exit: the value of the norm specified by norm.
7:     fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INT
On entry, n=value.
Constraint: n0.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

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

nag_dsp_norm (f16rdc) is not threaded in any implementation.

9
Further Comments

None.

10
Example

See Section 10 in nag_dppcon (f07ggc) and nag_dspcon (f07pgc).
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017