# sgelsx.f man page

sgelsx.f —

## Synopsis

### Functions/Subroutines

subroutinesgelsx(M, N, NRHS, A, LDA, B, LDB, JPVT, RCOND, RANK, WORK, INFO)SGELSX solves overdetermined or underdetermined systems for GE matrices

## Function/Subroutine Documentation

### subroutine sgelsx (integerM, integerN, integerNRHS, real, dimension( lda, * )A, integerLDA, real, dimension( ldb, * )B, integerLDB, integer, dimension( * )JPVT, realRCOND, integerRANK, real, dimension( * )WORK, integerINFO)

**SGELSX solves overdetermined or underdetermined systems for GE matrices**

**Purpose:**

```
This routine is deprecated and has been replaced by routine SGELSY.
SGELSX computes the minimum-norm solution to a real linear least
squares problem:
minimize || A * X - B ||
using a complete orthogonal factorization of A. A is an M-by-N
matrix which may be rank-deficient.
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
M-by-NRHS right hand side matrix B and the N-by-NRHS solution
matrix X.
The routine first computes a QR factorization with column pivoting:
A * P = Q * [ R11 R12 ]
[ 0 R22 ]
with R11 defined as the largest leading submatrix whose estimated
condition number is less than 1/RCOND. The order of R11, RANK,
is the effective rank of A.
Then, R22 is considered to be negligible, and R12 is annihilated
by orthogonal transformations from the right, arriving at the
complete orthogonal factorization:
A * P = Q * [ T11 0 ] * Z
[ 0 0 ]
The minimum-norm solution is then
X = P * Z**T [ inv(T11)*Q1**T*B ]
[ 0 ]
where Q1 consists of the first RANK columns of Q.
```

**Parameters:**

*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 matrices B and X. NRHS >= 0.
```

*A*

```
A is REAL array, dimension (LDA,N)
On entry, the M-by-N matrix A.
On exit, A has been overwritten by details of its
complete orthogonal factorization.
```

*LDA*

```
LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,M).
```

*B*

```
B is REAL array, dimension (LDB,NRHS)
On entry, the M-by-NRHS right hand side matrix B.
On exit, the N-by-NRHS solution matrix X.
If m >= n and RANK = n, the residual sum-of-squares for
the solution in the i-th column is given by the sum of
squares of elements N+1:M in that column.
```

*LDB*

```
LDB is INTEGER
The leading dimension of the array B. LDB >= max(1,M,N).
```

*JPVT*

```
JPVT is INTEGER array, dimension (N)
On entry, if JPVT(i) .ne. 0, the i-th column of A is an
initial column, otherwise it is a free column. Before
the QR factorization of A, all initial columns are
permuted to the leading positions; only the remaining
free columns are moved as a result of column pivoting
during the factorization.
On exit, if JPVT(i) = k, then the i-th column of A*P
was the k-th column of A.
```

*RCOND*

```
RCOND is REAL
RCOND is used to determine the effective rank of A, which
is defined as the order of the largest leading triangular
submatrix R11 in the QR factorization with pivoting of A,
whose estimated condition number < 1/RCOND.
```

*RANK*

```
RANK is INTEGER
The effective rank of A, i.e., the order of the submatrix
R11. This is the same as the order of the submatrix T11
in the complete orthogonal factorization of A.
```

*WORK*

```
WORK is REAL array, dimension
(max( min(M,N)+3*N, 2*min(M,N)+NRHS )),
```

*INFO*

```
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

Definition at line 178 of file sgelsx.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

sgelsx(3) is an alias of sgelsx.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK