# claed0.f man page

claed0.f —

## Synopsis

### Functions/Subroutines

subroutineclaed0(QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, RWORK, IWORK, INFO)CLAED0used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

## Function/Subroutine Documentation

### subroutine claed0 (integerQSIZ, integerN, real, dimension( * )D, real, dimension( * )E, complex, dimension( ldq, * )Q, integerLDQ, complex, dimension( ldqs, * )QSTORE, integerLDQS, real, dimension( * )RWORK, integer, dimension( * )IWORK, integerINFO)

**CLAED0** used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

**Purpose:**

```
Using the divide and conquer method, CLAED0 computes all eigenvalues
of a symmetric tridiagonal matrix which is one diagonal block of
those from reducing a dense or band Hermitian matrix and
corresponding eigenvectors of the dense or band matrix.
```

**Parameters:**

*QSIZ*

```
QSIZ is INTEGER
The dimension of the unitary matrix used to reduce
the full matrix to tridiagonal form. QSIZ >= N if ICOMPQ = 1.
```

*N*

```
N is INTEGER
The dimension of the symmetric tridiagonal matrix. N >= 0.
```

*D*

```
D is REAL array, dimension (N)
On entry, the diagonal elements of the tridiagonal matrix.
On exit, the eigenvalues in ascending order.
```

*E*

```
E is REAL array, dimension (N-1)
On entry, the off-diagonal elements of the tridiagonal matrix.
On exit, E has been destroyed.
```

*Q*

```
Q is COMPLEX array, dimension (LDQ,N)
On entry, Q must contain an QSIZ x N matrix whose columns
unitarily orthonormal. It is a part of the unitary matrix
that reduces the full dense Hermitian matrix to a
(reducible) symmetric tridiagonal matrix.
```

*LDQ*

```
LDQ is INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
```

*IWORK*

```
IWORK is INTEGER array,
the dimension of IWORK must be at least
6 + 6*N + 5*N*lg N
( lg( N ) = smallest integer k
such that 2^k >= N )
```

*RWORK*

```
RWORK is REAL array,
dimension (1 + 3*N + 2*N*lg N + 3*N**2)
( lg( N ) = smallest integer k
such that 2^k >= N )
```

*QSTORE*

```
QSTORE is COMPLEX array, dimension (LDQS, N)
Used to store parts of
the eigenvector matrix when the updating matrix multiplies
take place.
```

*LDQS*

```
LDQS is INTEGER
The leading dimension of the array QSTORE.
LDQS >= max(1,N).
```

*INFO*

```
INFO is INTEGER
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
> 0: The algorithm failed to compute an eigenvalue while
working on the submatrix lying in rows and columns
INFO/(N+1) through mod(INFO,N+1).
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

Definition at line 145 of file claed0.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

claed0(3) is an alias of claed0.f(3).