dpoequ.f(3) LAPACK dpoequ.f(3)
subroutine dpoequ (N, A, LDA, S, SCOND, AMAX, INFO)
subroutine dpoequ (integerN, double precision, dimension( lda, * )A, integerLDA, double
precision, dimension( * )S, double precisionSCOND, double precisionAMAX, integerINFO)
DPOEQU computes row and column scalings intended to equilibrate a
symmetric positive definite 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
N is INTEGER
The order of the matrix A. N >= 0.
A is DOUBLE PRECISION array, dimension (LDA,N)
The N-by-N symmetric positive definite matrix whose scaling
factors are to be computed. Only the diagonal elements of A
LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,N).
S is DOUBLE PRECISION array, dimension (N)
If INFO = 0, S contains the scale factors for A.
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 is DOUBLE PRECISION
Absolute value of largest matrix element. If AMAX is very
close to overflow or very close to underflow, the matrix
should be scaled.
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.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
Definition at line 113 of file dpoequ.f.
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Version 3.4.2 Tue Sep 25 2012 dpoequ.f(3)