Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?laed4
Used by sstedc / dstedc . Finds a single root of the secular equation.
Syntax
call slaed4 ( n , i , d , z , delta , rho , dlam , info )
call dlaed4 ( n , i , d , z , delta , rho , dlam , info )
Include Files
mkl.fi
Description
slaed4 dlaed4
This routine computes the i -th updated eigenvalue of a symmetric rank-one modification to a diagonal matrix whose elements are given in the array d , and that
D(i) < D(j) for i < j
and that rho > 0 . This is arranged by the calling routine, and is no loss in generality. The rank-one modified system is thus
diag(D) + rho*Z * transpose(Z) .
where we assume the Euclidean norm of Z is 1.
The method consists of approximating the rational functions in the secular equation by simpler interpolating rational functions.
Input Parameters
- n
-
INTEGER . The length of all arrays.
- i
-
INTEGER . The index of the eigenvalue to be computed; 1 ≤ i ≤ n .
- d , z
-
REAL for slaed4 DOUBLE PRECISION for dlaed4 Arrays, dimension ( n ) each. The array d contains the original eigenvalues. It is assumed that they are in order, d(i) < d(j) for i < j . The array z contains the components of the updating vector Z .
- rho
-
REAL for slaed4 DOUBLE PRECISION for dlaed4 The scalar in the symmetric updating formula.
Output Parameters
- delta
-
REAL for slaed4 DOUBLE PRECISION for dlaed4 Array, dimension ( n ). If n≠ 1 , delta contains ( d(j) - lambda_i ) in its j -th component. If n = 1 , then delta(1) = 1 . The vector delta contains the information necessary to construct the eigenvectors.
- dlam
-
REAL for slaed4 DOUBLE PRECISION for dlaed4 The computed lambda_i , the i -th updated eigenvalue.
info
INTEGER .
If info = 0 , the execution is successful.
If info = 1 , the updating process failed.