---
name: "dstev"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/dstev/3lapack"
---

# dstev(3lapack)

computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A

## NAME

DSTEV - computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A

## SYNOPSIS

- SUBROUTINE DSTEV(

  JOBZ, N, D, E, Z, LDZ, WORK, INFO )

- CHARACTER

  JOBZ

- INTEGER

  INFO, LDZ, N

- DOUBLE

  PRECISION D( \* ), E( \* ), WORK( \* ), Z( LDZ, \* )

## PURPOSE

DSTEV computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.

## ARGUMENTS

- JOBZ (input) CHARACTER\*1

  \= 'N':  Compute eigenvalues only;\
   \= 'V':  Compute eigenvalues and eigenvectors.

- N (input) INTEGER

  The order of the matrix.  N \>= 0.

- D (input/output) DOUBLE PRECISION array, dimension (N)

  On entry, the n diagonal elements of the tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues in ascending order.

- E (input/output) DOUBLE PRECISION array, dimension (N-1)

  On entry, the (n-1) subdiagonal elements of the tridiagonal matrix A, stored in elements 1 to N-1 of E. On exit, the contents of E are destroyed.

- Z (output) DOUBLE PRECISION array, dimension (LDZ, N)

  If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal eigenvectors of the matrix A, with the i-th column of Z holding the eigenvector associated with D(i). If JOBZ = 'N', then Z is not referenced.

- LDZ (input) INTEGER

  The leading dimension of the array Z.  LDZ \>= 1, and if JOBZ = 'V', LDZ \>= max(1,N).

- WORK (workspace) DOUBLE PRECISION array, dimension (max(1,2\*N-2))

  If JOBZ = 'N', WORK is not referenced.

- INFO (output) INTEGER

  \= 0:  successful exit\
   \< 0:  if INFO = -i, the i-th argument had an illegal value\
   \> 0:  if INFO = i, the algorithm failed to converge; i off-diagonal elements of E did not converge to zero.