cheequb.f (3) Linux Manual Page

cheequb.f –

Synopsis

Functions/Subroutines

subroutine cheequb (UPLO, N, A, LDA, S, SCOND, AMAX, WORK, INFO)
CHEEQUB

Function/Subroutine Documentation

subroutine cheequb (characterUPLO, integerN, complex, dimension( lda, * )A, integerLDA, real, dimension( * )S, realSCOND, realAMAX, complex, dimension( * )WORK, integerINFO)

CHEEQUB

Purpose:

 CHEEQUB computes row and column scalings intended to equilibrate a

 Hermitian matrix A and reduce its condition number

 (with respect to the two-norm). S contains the scale factors,

 S(i) = 1/sqrt(A(i,i)), chosen so that the scaled matrix B with

 elements B(i,j) = S(i)*A(i,j)*S(j) has ones on the diagonal. This

 choice of S puts the condition number of B within a factor N of the

 smallest possible condition number over all possible diagonal

 scalings.

 

Parameters:

UPLO

 UPLO is CHARACTER*1

 = ‘U’: Upper triangles of A and B are stored;

 = ‘L’: Lower triangles of A and B are stored.

N

 N is INTEGER

 The order of the matrix A. N >= 0.

A

 A is COMPLEX array, dimension (LDA,N)

 The N-by-N Hermitian matrix whose scaling

 factors are to be computed. Only the diagonal elements of A

 are referenced.

LDA

 LDA is INTEGER

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

S

 S is REAL array, dimension (N)

 If INFO = 0, S contains the scale factors for A.

SCOND

 SCOND is REAL

 If INFO = 0, S contains the ratio of the smallest S(i) to

 the largest S(i). If SCOND >= 0.1 and AMAX is neither too

 large nor too small, it is not worth scaling by S.

AMAX

 AMAX is REAL

 Absolute value of largest matrix element. If AMAX is very

 close to overflow or very close to underflow, the matrix

 should be scaled.

WORK

 WORK is COMPLEX array, dimension (3*N)

INFO

 INFO is INTEGER

 = 0: successful exit

 < 0: if INFO = -i, the i-th argument had an illegal value

 > 0: if INFO = i, the i-th diagonal element is nonpositive.

 

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

April 2012

Definition at line 127 of file cheequb.f.

Author

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