# dlasd0.f man page

dlasd0.f —

## Synopsis

### Functions/Subroutines

subroutinedlasd0(N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK, WORK, INFO)DLASD0computes 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 (integerN, integerSQRE, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension( ldu, * )U, integerLDU, double precision, dimension( ldvt, * )VT, integerLDVT, integerSMLSIZ, integer, dimension( * )IWORK, double precision, dimension( * )WORK, integerINFO)

**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 at least (LDQ, N)
On exit, U contains the left singular vectors.
```

*LDU*

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

*VT*

```
VT is DOUBLE PRECISION array, dimension at least (LDVT, M)
On exit, VT**T contains the right singular vectors.
```

*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 work array.
Dimension must be at least (8 * N)
```

*WORK*

```
WORK is DOUBLE PRECISION work array.
Dimension must be at least (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.

**Date:**

September 2012

**Contributors:**

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

Definition at line 152 of file dlasd0.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dlasd0(3) is an alias of dlasd0.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK