Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?laneg
Computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T - sigma * I = L * D * L:code:`T` .
Syntax
valueslaneg ( n , d , lld , sigma , pivmin , r )
valuedlaneg ( n , d , lld , sigma , pivmin , r )
Include Files
mkl.fi
Description
slaneg dlaneg
The routine computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T - sigma * I = L * D * L:code:`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 ?larb . The current routine does not use the pivmin parameter but rather requires IEEE-754 propagation of infinities and NaN s ( NaN stands for ‘Not A Number’). This routine also has no input range restrictions but does require default exception handling such that x/0 produces Inf when x is non-zero, and Inf/Inf produces NaN . (For more information see [Marques06]).
Input Parameters
- n
-
INTEGER . The order of the matrix.
- d
-
REAL for slaneg DOUBLE PRECISION for dlaneg Array, DIMENSION ( n ). Contains n diagonal elements of the matrix D .
- lld
-
REAL for slaneg DOUBLE PRECISION for dlaneg Array, DIMENSION ( n-1 ). Contains (n-1) elements L(i)*L(i)*D(i) .
- sigma
-
REAL for slaneg DOUBLE PRECISION for dlaneg Shift amount in T-sigma*I = L*D*L**T .
- pivmin
-
REAL for slaneg DOUBLE PRECISION for dlaneg The minimum pivot in the Sturm sequence. May be used when zero pivots are encountered on non-IEEE-754 architectures.
- r
-
INTEGER . The twist index for the twisted factorization that is used for the negcount.
Output Parameters
- value
-
INTEGER . The number of negative pivots encountered while factoring.