subroutine dsyequb (UPLO, N, A, LDA, S, SCOND, AMAX, WORK, INFO)
DSYEQUB
DSYEQUB
Purpose:
DSYEQUB computes row and column scalings intended to equilibrate a symmetric matrix A (with respect to the Euclidean norm) and reduce its condition number. The scale factors S are computed by the BIN algorithm (see references) so that the scaled matrix B with elements B(i,j) = S(i)*A(i,j)*S(j) has a condition number within a factor N of the smallest possible condition number over all possible diagonal scalings.
Parameters:
UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.
N
N is INTEGER The order of the matrix A. N >= 0.
A
A is DOUBLE PRECISION array, dimension (LDA,N) The N-by-N symmetric matrix whose scaling factors are to be computed.
LDA
LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).
S
S is DOUBLE PRECISION array, dimension (N) If INFO = 0, S contains the scale factors for A.
SCOND
SCOND is DOUBLE PRECISION 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 DOUBLE PRECISION Largest absolute value of any matrix element. If AMAX is very close to overflow or very close to underflow, the matrix should be scaled.
WORK
WORK is DOUBLE PRECISION array, dimension (2*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 California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
References:
Definition at line 133 of file dsyequb.f.
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