slarra.f (3) - Linux Man Pages
subroutine slarra (integerN, real, dimension( * )D, real, dimension( * )E, real, dimension( * )E2, realSPLTOL, realTNRM, integerNSPLIT, integer, dimension( * )ISPLIT, integerINFO)
SLARRA computes the splitting points with the specified threshold.
Compute the splitting points with threshold SPLTOL. SLARRA sets any "small" off-diagonal elements to zero.
N is INTEGER The order of the matrix. N > 0.
D is REAL array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T.
E is REAL array, dimension (N) On entry, the first (N-1) entries contain the subdiagonal elements of the tridiagonal matrix T; E(N) need not be set. On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT, are set to zero, the other entries of E are untouched.
E2 is REAL array, dimension (N) On entry, the first (N-1) entries contain the SQUARES of the subdiagonal elements of the tridiagonal matrix T; E2(N) need not be set. On exit, the entries E2( ISPLIT( I ) ), 1 <= I <= NSPLIT, have been set to zero
SPLTOL is REAL The threshold for splitting. Two criteria can be used: SPLTOL<0 : criterion based on absolute off-diagonal value SPLTOL>0 : criterion that preserves relative accuracy
TNRM is REAL The norm of the matrix.
NSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N.
ISPLIT is INTEGER array, dimension (N) The splitting points, at which T breaks up into blocks. The first block consists of rows/columns 1 to ISPLIT(1), the second of rows/columns ISPLIT(1)+1 through ISPLIT(2), etc., and the NSPLIT-th consists of rows/columns ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.
INFO is INTEGER = 0: successful exit
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
- September 2012
Beresford Parlett, University of California, Berkeley, USA
Jim Demmel, University of California, Berkeley, USA
Inderjit Dhillon, University of Texas, Austin, USA
Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
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