## Linux and UNIX Man Pages

Test Your Knowledge in Computers #671
Difficulty: Medium
DOS primarily consists of Microsoft's MS-DOS and a rebranded IBM version under the name PC DOS, both of which were introduced in 1981.
True or False?

# dlalsd.f(3) [centos man page]

```dlalsd.f(3)							      LAPACK							       dlalsd.f(3)

NAME
dlalsd.f -

SYNOPSIS
Functions/Subroutines
subroutine dlalsd (UPLO, SMLSIZ, N, NRHS, D, E, B, LDB, RCOND, RANK, WORK, IWORK, INFO)
DLALSD uses the singular value decomposition of A to solve the least squares problem.

Function/Subroutine Documentation
subroutine dlalsd (characterUPLO, integerSMLSIZ, integerN, integerNRHS, double precision, dimension( * )D, double precision, dimension( * )E,
double precision, dimension( ldb, * )B, integerLDB, double precisionRCOND, integerRANK, double precision, dimension( * )WORK, integer,
dimension( * )IWORK, integerINFO)
DLALSD uses the singular value decomposition of A to solve the least squares problem.

Purpose:

DLALSD uses the singular value decomposition of A to solve the least
squares problem of finding X to minimize the Euclidean norm of each
column of A*X-B, where A is N-by-N upper bidiagonal, and X and B
are N-by-NRHS. The solution X overwrites B.

The singular values of A smaller than RCOND times the largest
singular value are treated as zero in solving the least squares
problem; in this case a minimum norm solution is returned.
The actual singular values are returned in D in ascending order.

This code makes very mild assumptions about floating point
arithmetic. It will work on machines with a guard digit in
add/subtract, or on those binary machines without guard digits
which subtract like the Cray XMP, Cray YMP, Cray C 90, or Cray 2.
It could conceivably fail on hexadecimal or decimal machines
without guard digits, but we know of none.

Parameters:
UPLO

UPLO is CHARACTER*1
= 'U': D and E define an upper bidiagonal matrix.
= 'L': D and E define a  lower bidiagonal matrix.

SMLSIZ

SMLSIZ is INTEGER
The maximum size of the subproblems at the bottom of the
computation tree.

N

N is INTEGER
The dimension of the  bidiagonal matrix.  N >= 0.

NRHS

NRHS is INTEGER
The number of columns of B. NRHS must be at least 1.

D

D is DOUBLE PRECISION array, dimension (N)
On entry D contains the main diagonal of the bidiagonal
matrix. On exit, if INFO = 0, D contains its singular values.

E

E is DOUBLE PRECISION array, dimension (N-1)
Contains the super-diagonal entries of the bidiagonal matrix.
On exit, E has been destroyed.

B

B is DOUBLE PRECISION array, dimension (LDB,NRHS)
On input, B contains the right hand sides of the least
squares problem. On output, B contains the solution X.

LDB

LDB is INTEGER
The leading dimension of B in the calling subprogram.
LDB must be at least max(1,N).

RCOND

RCOND is DOUBLE PRECISION
The singular values of A less than or equal to RCOND times
the largest singular value are treated as zero in solving
the least squares problem. If RCOND is negative,
machine precision is used instead.
For example, if diag(S)*X=B were the least squares problem,
where diag(S) is a diagonal matrix of singular values, the
solution would be X(i) = B(i) / S(i) if S(i) is greater than
RCOND*max(S), and X(i) = 0 if S(i) is less than or equal to
RCOND*max(S).

RANK

RANK is INTEGER
The number of singular values of A greater than RCOND times
the largest singular value.

WORK

WORK is DOUBLE PRECISION array, dimension at least
(9*N + 2*N*SMLSIZ + 8*N*NLVL + N*NRHS + (SMLSIZ+1)**2),
where NLVL = max(0, INT(log_2 (N/(SMLSIZ+1))) + 1).

IWORK

IWORK is INTEGER array, dimension at least
(3*N*NLVL + 11*N)

INFO

INFO is INTEGER
= 0:  successful exit.
< 0:  if INFO = -i, the i-th argument had an illegal value.
> 0:  The algorithm failed to compute a singular value while
working on the submatrix lying in rows and columns
INFO/(N+1) through MOD(INFO,N+1).

Author:
Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:
September 2012

Contributors:
Ming Gu and Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA
Osni Marques, LBNL/NERSC, USA

Definition at line 179 of file dlalsd.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       dlalsd.f(3)```