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---
:name: slarra
:md5sum: 8c265e4b5b823f839c614ef3bc019488
:category: :subroutine
:arguments:
- n:
:type: integer
:intent: input
- d:
:type: real
:intent: input
:dims:
- n
- e:
:type: real
:intent: input/output
:dims:
- n
- e2:
:type: real
:intent: input/output
:dims:
- n
- spltol:
:type: real
:intent: input
- tnrm:
:type: real
:intent: input
- nsplit:
:type: integer
:intent: output
- isplit:
:type: integer
:intent: output
:dims:
- n
- info:
:type: integer
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE SLARRA( N, D, E, E2, SPLTOL, TNRM, NSPLIT, ISPLIT, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* Compute the splitting points with threshold SPLTOL.\n\
* SLARRA sets any \"small\" off-diagonal elements to zero.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* N (input) INTEGER\n\
* The order of the matrix. N > 0.\n\
*\n\
* D (input) REAL array, dimension (N)\n\
* On entry, the N diagonal elements of the tridiagonal\n\
* matrix T.\n\
*\n\
* E (input/output) REAL array, dimension (N)\n\
* On entry, the first (N-1) entries contain the subdiagonal\n\
* elements of the tridiagonal matrix T; E(N) need not be set.\n\
* On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT,\n\
* are set to zero, the other entries of E are untouched.\n\
*\n\
* E2 (input/output) REAL array, dimension (N)\n\
* On entry, the first (N-1) entries contain the SQUARES of the\n\
* subdiagonal elements of the tridiagonal matrix T;\n\
* E2(N) need not be set.\n\
* On exit, the entries E2( ISPLIT( I ) ),\n\
* 1 <= I <= NSPLIT, have been set to zero\n\
*\n\
* SPLTOL (input) REAL \n\
* The threshold for splitting. Two criteria can be used:\n\
* SPLTOL<0 : criterion based on absolute off-diagonal value\n\
* SPLTOL>0 : criterion that preserves relative accuracy\n\
*\n\
* TNRM (input) REAL \n\
* The norm of the matrix.\n\
*\n\
* NSPLIT (output) INTEGER\n\
* The number of blocks T splits into. 1 <= NSPLIT <= N.\n\
*\n\
* ISPLIT (output) INTEGER array, dimension (N)\n\
* The splitting points, at which T breaks up into blocks.\n\
* The first block consists of rows/columns 1 to ISPLIT(1),\n\
* the second of rows/columns ISPLIT(1)+1 through ISPLIT(2),\n\
* etc., and the NSPLIT-th consists of rows/columns\n\
* ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.\n\
*\n\
*\n\
* INFO (output) INTEGER\n\
* = 0: successful exit\n\
*\n\n\
* Further Details\n\
* ===============\n\
*\n\
* Based on contributions by\n\
* Beresford Parlett, University of California, Berkeley, USA\n\
* Jim Demmel, University of California, Berkeley, USA\n\
* Inderjit Dhillon, University of Texas, Austin, USA\n\
* Osni Marques, LBNL/NERSC, USA\n\
* Christof Voemel, University of California, Berkeley, USA\n\
*\n\
* =====================================================================\n\
*\n"
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