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---
:name: ssteqr
:md5sum: 75323c7177adfd9bb0df92567a13acaf
:category: :subroutine
:arguments:
- compz:
:type: char
:intent: input
- n:
:type: integer
:intent: input
- d:
:type: real
:intent: input/output
:dims:
- n
- e:
:type: real
:intent: input/output
:dims:
- n-1
- z:
:type: real
:intent: input/output
:dims:
- ldz
- n
- ldz:
:type: integer
:intent: input
- work:
:type: real
:intent: workspace
:dims:
- "lsame_(&compz,\"N\") ? 0 : MAX(1,2*n-2)"
- info:
:type: integer
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE SSTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* SSTEQR computes all eigenvalues and, optionally, eigenvectors of a\n\
* symmetric tridiagonal matrix using the implicit QL or QR method.\n\
* The eigenvectors of a full or band symmetric matrix can also be found\n\
* if SSYTRD or SSPTRD or SSBTRD has been used to reduce this matrix to\n\
* tridiagonal form.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* COMPZ (input) CHARACTER*1\n\
* = 'N': Compute eigenvalues only.\n\
* = 'V': Compute eigenvalues and eigenvectors of the original\n\
* symmetric matrix. On entry, Z must contain the\n\
* orthogonal matrix used to reduce the original matrix\n\
* to tridiagonal form.\n\
* = 'I': Compute eigenvalues and eigenvectors of the\n\
* tridiagonal matrix. Z is initialized to the identity\n\
* matrix.\n\
*\n\
* N (input) INTEGER\n\
* The order of the matrix. N >= 0.\n\
*\n\
* D (input/output) REAL array, dimension (N)\n\
* On entry, the diagonal elements of the tridiagonal matrix.\n\
* On exit, if INFO = 0, the eigenvalues in ascending order.\n\
*\n\
* E (input/output) REAL array, dimension (N-1)\n\
* On entry, the (n-1) subdiagonal elements of the tridiagonal\n\
* matrix.\n\
* On exit, E has been destroyed.\n\
*\n\
* Z (input/output) REAL array, dimension (LDZ, N)\n\
* On entry, if COMPZ = 'V', then Z contains the orthogonal\n\
* matrix used in the reduction to tridiagonal form.\n\
* On exit, if INFO = 0, then if COMPZ = 'V', Z contains the\n\
* orthonormal eigenvectors of the original symmetric matrix,\n\
* and if COMPZ = 'I', Z contains the orthonormal eigenvectors\n\
* of the symmetric tridiagonal matrix.\n\
* If COMPZ = 'N', then Z is not referenced.\n\
*\n\
* LDZ (input) INTEGER\n\
* The leading dimension of the array Z. LDZ >= 1, and if\n\
* eigenvectors are desired, then LDZ >= max(1,N).\n\
*\n\
* WORK (workspace) REAL array, dimension (max(1,2*N-2))\n\
* If COMPZ = 'N', then WORK is not referenced.\n\
*\n\
* INFO (output) INTEGER\n\
* = 0: successful exit\n\
* < 0: if INFO = -i, the i-th argument had an illegal value\n\
* > 0: the algorithm has failed to find all the eigenvalues in\n\
* a total of 30*N iterations; if INFO = i, then i\n\
* elements of E have not converged to zero; on exit, D\n\
* and E contain the elements of a symmetric tridiagonal\n\
* matrix which is orthogonally similar to the original\n\
* matrix.\n\
*\n\n\
* =====================================================================\n\
*\n"
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