larra - larra: step in stemr

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subroutinedlarra(integern,doubleprecision,dimension(*)d,doubleprecision,dimension(*)e,doubleprecision,dimension(*)e2,doubleprecisionspltol,doubleprecisiontnrm,integernsplit,integer,dimension(*)isplit,integerinfo)DLARRA computes the splitting points with the specified threshold. Purpose: Compute the splitting points with threshold SPLTOL. DLARRA sets any 'small' off-diagonal elements to zero. ParametersN N is INTEGER The order of the matrix. N > 0. D D is DOUBLE PRECISION array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T. E E is DOUBLE PRECISION 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 E2 is DOUBLE PRECISION 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 SPLTOL is DOUBLE PRECISION 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 TNRM is DOUBLE PRECISION The norm of the matrix. NSPLIT NSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N. 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. INFO INFO is INTEGER = 0: successful exit Author Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd. Contributors: 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 subroutineslarra(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. Purpose: Compute the splitting points with threshold SPLTOL. SLARRA sets any 'small' off-diagonal elements to zero. ParametersN N is INTEGER The order of the matrix. N > 0. D D is REAL array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T. 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. 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 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 TNRM TNRM is REAL The norm of the matrix. NSPLIT NSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N. 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. INFO INFO is INTEGER = 0: successful exit Author Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd. Contributors: 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

larra - larra: step in stemr

Functions subroutine dlarra (n, d, e, e2, spltol, tnrm, nsplit, isplit, info) DLARRA computes the splitting points with the specified threshold. subroutine slarra (n, d, e, e2, spltol, tnrm, nsplit, isplit, info) SLARRA computes the splitting points with the specified threshold.