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---
:name: dlaed0
:md5sum: 337ae89b96bbbde72236a7ce62eb8536
:category: :subroutine
:arguments:
- icompq:
:type: integer
:intent: input
- qsiz:
:type: integer
:intent: input
- n:
:type: integer
:intent: input
- d:
:type: doublereal
:intent: input/output
:dims:
- n
- e:
:type: doublereal
:intent: input
:dims:
- n-1
- q:
:type: doublereal
:intent: input/output
:dims:
- ldq
- n
- ldq:
:type: integer
:intent: input
- qstore:
:type: doublereal
:intent: workspace
:dims:
- ldqs
- n
- ldqs:
:type: integer
:intent: input
- work:
:type: doublereal
:intent: workspace
:dims:
- "((icompq == 0) || (icompq == 1)) ? 1 + 3*n + 2*n*LG(n) + 2*pow(n,2) : icompq == 2 ? 4*n + pow(n,2) : 0"
- iwork:
:type: integer
:intent: workspace
:dims:
- "((icompq == 0) || (icompq == 1)) ? 6 + 6*n + 5*n*LG(n) : icompq == 2 ? 3 + 5*n : 0"
- info:
:type: integer
:intent: output
:substitutions:
ldqs: "icompq == 1 ? MAX(1,n) : 1"
:fortran_help: " SUBROUTINE DLAED0( ICOMPQ, QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, WORK, IWORK, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* DLAED0 computes all eigenvalues and corresponding eigenvectors of a\n\
* symmetric tridiagonal matrix using the divide and conquer method.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* ICOMPQ (input) INTEGER\n\
* = 0: Compute eigenvalues only.\n\
* = 1: Compute eigenvectors of original dense symmetric matrix\n\
* also. On entry, Q contains the orthogonal matrix used\n\
* to reduce the original matrix to tridiagonal form.\n\
* = 2: Compute eigenvalues and eigenvectors of tridiagonal\n\
* matrix.\n\
*\n\
* QSIZ (input) INTEGER\n\
* The dimension of the orthogonal matrix used to reduce\n\
* the full matrix to tridiagonal form. QSIZ >= N if ICOMPQ = 1.\n\
*\n\
* N (input) INTEGER\n\
* The dimension of the symmetric tridiagonal matrix. N >= 0.\n\
*\n\
* D (input/output) DOUBLE PRECISION array, dimension (N)\n\
* On entry, the main diagonal of the tridiagonal matrix.\n\
* On exit, its eigenvalues.\n\
*\n\
* E (input) DOUBLE PRECISION array, dimension (N-1)\n\
* The off-diagonal elements of the tridiagonal matrix.\n\
* On exit, E has been destroyed.\n\
*\n\
* Q (input/output) DOUBLE PRECISION array, dimension (LDQ, N)\n\
* On entry, Q must contain an N-by-N orthogonal matrix.\n\
* If ICOMPQ = 0 Q is not referenced.\n\
* If ICOMPQ = 1 On entry, Q is a subset of the columns of the\n\
* orthogonal matrix used to reduce the full\n\
* matrix to tridiagonal form corresponding to\n\
* the subset of the full matrix which is being\n\
* decomposed at this time.\n\
* If ICOMPQ = 2 On entry, Q will be the identity matrix.\n\
* On exit, Q contains the eigenvectors of the\n\
* tridiagonal matrix.\n\
*\n\
* LDQ (input) INTEGER\n\
* The leading dimension of the array Q. If eigenvectors are\n\
* desired, then LDQ >= max(1,N). In any case, LDQ >= 1.\n\
*\n\
* QSTORE (workspace) DOUBLE PRECISION array, dimension (LDQS, N)\n\
* Referenced only when ICOMPQ = 1. Used to store parts of\n\
* the eigenvector matrix when the updating matrix multiplies\n\
* take place.\n\
*\n\
* LDQS (input) INTEGER\n\
* The leading dimension of the array QSTORE. If ICOMPQ = 1,\n\
* then LDQS >= max(1,N). In any case, LDQS >= 1.\n\
*\n\
* WORK (workspace) DOUBLE PRECISION array,\n\
* If ICOMPQ = 0 or 1, the dimension of WORK must be at least\n\
* 1 + 3*N + 2*N*lg N + 2*N**2\n\
* ( lg( N ) = smallest integer k\n\
* such that 2^k >= N )\n\
* If ICOMPQ = 2, the dimension of WORK must be at least\n\
* 4*N + N**2.\n\
*\n\
* IWORK (workspace) INTEGER array,\n\
* If ICOMPQ = 0 or 1, the dimension of IWORK must be at least\n\
* 6 + 6*N + 5*N*lg N.\n\
* ( lg( N ) = smallest integer k\n\
* such that 2^k >= N )\n\
* If ICOMPQ = 2, the dimension of IWORK must be at least\n\
* 3 + 5*N.\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 failed to compute an eigenvalue while\n\
* working on the submatrix lying in rows and columns\n\
* INFO/(N+1) through mod(INFO,N+1).\n\
*\n\n\
* Further Details\n\
* ===============\n\
*\n\
* Based on contributions by\n\
* Jeff Rutter, Computer Science Division, University of California\n\
* at Berkeley, USA\n\
*\n\
* =====================================================================\n\
*\n"
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