---
name: "claed0"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/claed0.f"
---

# claed0(3)

Part of [claed0.f(3)](/claed0.f/3.md).

## NAME

SRC/claed0.f

## SYNOPSIS

### Functions/Subroutines

subroutine **claed0** (qsiz, n, d, e, q, ldq, qstore, ldqs, rwork, iwork, info)\
 **CLAED0** used by CSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

## Function/Subroutine Documentation

### subroutine claed0 (integer qsiz, integer n, real, dimension( \* ) d, real, dimension( \* ) e, complex, dimension( ldq, \* ) q, integer ldq, complex, dimension( ldqs, \* ) qstore, integer ldqs, real, dimension( \* ) rwork, integer, dimension( \* ) iwork, integer info)

**CLAED0** used by CSTEDC. 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.

Definition at line **143** of file **claed0.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.