laneg#

Functions

INT slaneg(
    const INT  n,
    const f32* D,
    const f32* lld,
    const f32  sigma,
    const f32  pivmin,
    const INT  r
);
INT slaneg(const INT n, const f32 *D, const f32 *lld, const f32 sigma, const f32 pivmin, const INT r)#

SLANEG computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T - sigma I = L D L^T.

This implementation works directly on the factors without forming the tridiagonal matrix T. The Sturm count is also the number of eigenvalues of T less than sigma.

This routine is called from SLARRB.

The current routine does not use the PIVMIN parameter but rather requires IEEE-754 propagation of Infinities and NaNs.

Parameters

in
n

The order of the matrix.

in
D

Double precision array, dimension (n). The n diagonal elements of the diagonal matrix D.

in
lld

Double precision array, dimension (n-1). The (n-1) elements L(i)*L(i)*D(i).

in
sigma

Shift amount in T - sigma I = L D L^T.

in
pivmin

The minimum pivot in the Sturm sequence.

in
r

The twist index for the twisted factorization.

Functions

INT dlaneg(
    const INT  n,
    const f64* D,
    const f64* lld,
    const f64  sigma,
    const f64  pivmin,
    const INT  r
);
INT dlaneg(const INT n, const f64 *D, const f64 *lld, const f64 sigma, const f64 pivmin, const INT r)#

DLANEG computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T - sigma I = L D L^T.

This implementation works directly on the factors without forming the tridiagonal matrix T. The Sturm count is also the number of eigenvalues of T less than sigma.

This routine is called from DLARRB.

The current routine does not use the PIVMIN parameter but rather requires IEEE-754 propagation of Infinities and NaNs.

Parameters

in
n

The order of the matrix.

in
D

Double precision array, dimension (n). The n diagonal elements of the diagonal matrix D.

in
lld

Double precision array, dimension (n-1). The (n-1) elements L(i)*L(i)*D(i).

in
sigma

Shift amount in T - sigma I = L D L^T.

in
pivmin

The minimum pivot in the Sturm sequence.

in
r

The twist index for the twisted factorization.

On this page

This Page