# dlasd0.f - Man Page

SRC/dlasd0.f

## Synopsis

### Functions/Subroutines

subroutine dlasd0 (n, sqre, d, e, u, ldu, vt, ldvt, smlsiz, iwork, work, info)
DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc.

## Function/Subroutine Documentation

### subroutine dlasd0 (integer n, integer sqre, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldu, * ) u, integer ldu, double precision, dimension( ldvt, * ) vt, integer ldvt, integer smlsiz, integer, dimension( * ) iwork, double precision, dimension( * ) work, integer info)

DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc.

Purpose:

``` Using a divide and conquer approach, DLASD0 computes the singular
value decomposition (SVD) of a real upper bidiagonal N-by-M
matrix B with diagonal D and offdiagonal E, where M = N + SQRE.
The algorithm computes orthogonal matrices U and VT such that
B = U * S * VT. The singular values S are overwritten on D.

A related subroutine, DLASDA, computes only the singular values,
and optionally, the singular vectors in compact form.```
Parameters

N

```          N is INTEGER
On entry, the row dimension of the upper bidiagonal matrix.
This is also the dimension of the main diagonal array D.```

SQRE

```          SQRE is INTEGER
Specifies the column dimension of the bidiagonal matrix.
= 0: The bidiagonal matrix has column dimension M = N;
= 1: The bidiagonal matrix has column dimension M = N+1;```

D

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

E

```          E is DOUBLE PRECISION array, dimension (M-1)
Contains the subdiagonal entries of the bidiagonal matrix.
On exit, E has been destroyed.```

U

```          U is DOUBLE PRECISION array, dimension (LDU, N)
On exit, U contains the left singular vectors,
if U passed in as (N, N) Identity.```

LDU

```          LDU is INTEGER
On entry, leading dimension of U.```

VT

```          VT is DOUBLE PRECISION array, dimension (LDVT, M)
On exit, VT**T contains the right singular vectors,
if VT passed in as (M, M) Identity.```

LDVT

```          LDVT is INTEGER
On entry, leading dimension of VT.```

SMLSIZ

```          SMLSIZ is INTEGER
On entry, maximum size of the subproblems at the
bottom of the computation tree.```

IWORK

`          IWORK is INTEGER array, dimension (8*N)`

WORK

`          WORK is DOUBLE PRECISION array, dimension (3*M**2+2*M)`

INFO

```          INFO is INTEGER
= 0:  successful exit.
< 0:  if INFO = -i, the i-th argument had an illegal value.
> 0:  if INFO = 1, a singular value did not converge```
Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley, USA

Definition at line 150 of file dlasd0.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlasd0(3) is an alias of dlasd0.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK