LAPACK
3.6.1
LAPACK: Linear Algebra PACKage
|
subroutine slarra | ( | integer | N, |
real, dimension( * ) | D, | ||
real, dimension( * ) | E, | ||
real, dimension( * ) | E2, | ||
real | SPLTOL, | ||
real | TNRM, | ||
integer | NSPLIT, | ||
integer, dimension( * ) | ISPLIT, | ||
integer | INFO | ||
) |
SLARRA computes the splitting points with the specified threshold.
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Compute the splitting points with threshold SPLTOL. SLARRA sets any "small" off-diagonal elements to zero.
[in] | N | N is INTEGER The order of the matrix. N > 0. |
[in] | D | D is REAL array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T. |
[in,out] | E | 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. |
[in,out] | E2 | 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 |
[in] | SPLTOL | 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 |
[in] | TNRM | TNRM is REAL The norm of the matrix. |
[out] | NSPLIT | NSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N. |
[out] | ISPLIT | 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. |
[out] | INFO | INFO is INTEGER = 0: successful exit |
Definition at line 138 of file slarra.f.