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---
:name: dgeqr2
:md5sum: fb9ab1f2a4dd3ec44720edcbe890256c
:category: :subroutine
:arguments:
- m:
:type: integer
:intent: input
- n:
:type: integer
:intent: input
- a:
:type: doublereal
:intent: input/output
:dims:
- lda
- n
- lda:
:type: integer
:intent: input
- tau:
:type: doublereal
:intent: output
:dims:
- MIN(m,n)
- work:
:type: doublereal
:intent: workspace
:dims:
- n
- info:
:type: integer
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE DGEQR2( M, N, A, LDA, TAU, WORK, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* DGEQR2 computes a QR factorization of a real m by n matrix A:\n\
* A = Q * R.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* M (input) INTEGER\n\
* The number of rows of the matrix A. M >= 0.\n\
*\n\
* N (input) INTEGER\n\
* The number of columns of the matrix A. N >= 0.\n\
*\n\
* A (input/output) DOUBLE PRECISION array, dimension (LDA,N)\n\
* On entry, the m by n matrix A.\n\
* On exit, the elements on and above the diagonal of the array\n\
* contain the min(m,n) by n upper trapezoidal matrix R (R is\n\
* upper triangular if m >= n); the elements below the diagonal,\n\
* with the array TAU, represent the orthogonal matrix Q as a\n\
* product of elementary reflectors (see Further Details).\n\
*\n\
* LDA (input) INTEGER\n\
* The leading dimension of the array A. LDA >= max(1,M).\n\
*\n\
* TAU (output) DOUBLE PRECISION array, dimension (min(M,N))\n\
* The scalar factors of the elementary reflectors (see Further\n\
* Details).\n\
*\n\
* WORK (workspace) DOUBLE PRECISION array, dimension (N)\n\
*\n\
* INFO (output) INTEGER\n\
* = 0: successful exit\n\
* < 0: if INFO = -i, the i-th argument had an illegal value\n\
*\n\n\
* Further Details\n\
* ===============\n\
*\n\
* The matrix Q is represented as a product of elementary reflectors\n\
*\n\
* Q = H(1) H(2) . . . H(k), where k = min(m,n).\n\
*\n\
* Each H(i) has the form\n\
*\n\
* H(i) = I - tau * v * v'\n\
*\n\
* where tau is a real scalar, and v is a real vector with\n\
* v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),\n\
* and tau in TAU(i).\n\
*\n\
* =====================================================================\n\
*\n"
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