# dlasd0.f - Man Page

## 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.

*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.

*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.

**Date:**June 2017

**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

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

Tue Nov 14 2017 Version 3.8.0 LAPACK