
dgels.f(3) LAPACK dgels.f(3)
NAME
dgels.f 
SYNOPSIS
Functions/Subroutines
subroutine dgels (TRANS, M, N, NRHS, A, LDA, B, LDB, WORK, LWORK, INFO)
DGELS solves overdetermined or underdetermined systems for GE matrices
Function/Subroutine Documentation
subroutine dgels (characterTRANS, integerM, integerN, integerNRHS, double precision,
dimension( lda, * )A, integerLDA, double precision, dimension( ldb, * )B, integerLDB,
double precision, dimension( * )WORK, integerLWORK, integerINFO)
DGELS solves overdetermined or underdetermined systems for GE matrices
Purpose:
DGELS solves overdetermined or underdetermined real linear systems
involving an MbyN matrix A, or its transpose, using a QR or LQ
factorization of A. It is assumed that A has full rank.
The following options are provided:
1. If TRANS = 'N' and m >= n: find the least squares solution of
an overdetermined system, i.e., solve the least squares problem
minimize  B  A*X .
2. If TRANS = 'N' and m < n: find the minimum norm solution of
an underdetermined system A * X = B.
3. If TRANS = 'T' and m >= n: find the minimum norm solution of
an undetermined system A**T * X = B.
4. If TRANS = 'T' and m < n: find the least squares solution of
an overdetermined system, i.e., solve the least squares problem
minimize  B  A**T * X .
Several right hand side vectors b and solution vectors x can be
handled in a single call; they are stored as the columns of the
MbyNRHS right hand side matrix B and the NbyNRHS solution
matrix X.
Parameters:
TRANS
TRANS is CHARACTER*1
= 'N': the linear system involves A;
= 'T': the linear system involves A**T.
M
M is INTEGER
The number of rows of the matrix A. M >= 0.
N
N is INTEGER
The number of columns of the matrix A. N >= 0.
NRHS
NRHS is INTEGER
The number of right hand sides, i.e., the number of
columns of the matrices B and X. NRHS >=0.
A
A is DOUBLE PRECISION array, dimension (LDA,N)
On entry, the MbyN matrix A.
On exit,
if M >= N, A is overwritten by details of its QR
factorization as returned by DGEQRF;
if M < N, A is overwritten by details of its LQ
factorization as returned by DGELQF.
LDA
LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,M).
B
B is DOUBLE PRECISION array, dimension (LDB,NRHS)
On entry, the matrix B of right hand side vectors, stored
columnwise; B is MbyNRHS if TRANS = 'N', or NbyNRHS
if TRANS = 'T'.
On exit, if INFO = 0, B is overwritten by the solution
vectors, stored columnwise:
if TRANS = 'N' and m >= n, rows 1 to n of B contain the least
squares solution vectors; the residual sum of squares for the
solution in each column is given by the sum of squares of
elements N+1 to M in that column;
if TRANS = 'N' and m < n, rows 1 to N of B contain the
minimum norm solution vectors;
if TRANS = 'T' and m >= n, rows 1 to M of B contain the
minimum norm solution vectors;
if TRANS = 'T' and m < n, rows 1 to M of B contain the
least squares solution vectors; the residual sum of squares
for the solution in each column is given by the sum of
squares of elements M+1 to N in that column.
LDB
LDB is INTEGER
The leading dimension of the array B. LDB >= MAX(1,M,N).
WORK
WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK
LWORK is INTEGER
The dimension of the array WORK.
LWORK >= max( 1, MN + max( MN, NRHS ) ).
For optimal performance,
LWORK >= max( 1, MN + max( MN, NRHS )*NB ).
where MN = min(M,N) and NB is the optimum block size.
If LWORK = 1, then a workspace query is assumed; the routine
only calculates the optimal size of the WORK array, returns
this value as the first entry of the WORK array, and no error
message related to LWORK is issued by XERBLA.
INFO
INFO is INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, the ith diagonal element of the
triangular factor of A is zero, so that A does not have
full rank; the least squares solution could not be
computed.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 183 of file dgels.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dgels.f(3) 
