slasd5.f (3) - Linux Man Pages
subroutine slasd5 (integerI, real, dimension( 2 )D, real, dimension( 2 )Z, real, dimension( 2 )DELTA, realRHO, realDSIGMA, real, dimension( 2 )WORK)
SLASD5 computes the square root of the i-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix. Used by sbdsdc.
This subroutine computes the square root of the I-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix diag( D ) * diag( D ) + RHO * Z * transpose(Z) . The diagonal entries in the array D are assumed to satisfy 0 <= D(i) < D(j) for i < j . We also assume RHO > 0 and that the Euclidean norm of the vector Z is one.
I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2.
Z is REAL array, dimension (2) The components of the updating vector.
DELTA is REAL array, dimension (2) Contains (D(j) - sigma_I) in its j-th component. The vector DELTA contains the information necessary to construct the eigenvectors.
RHO is REAL The scalar in the symmetric updating formula.
DSIGMA is REAL The computed sigma_I, the I-th updated eigenvalue.
WORK is REAL array, dimension (2) WORK contains (D(j) + sigma_I) in its j-th component.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
- September 2012
- Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA
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