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- DGEQR2 - compute a QR factorization of a real m by n matrix A
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- SUBROUTINE DGEQR2( M, N, A, LDA, TAU, WORK, INFO )
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- INTEGER INFO, LDA, M, N
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- DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
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- These routines are part of the SCSL Scientific Library and can be loaded
- using either the -lscs or the -lscs_mp option. The -lscs_mp option
- directs the linker to use the multi-processor version of the library.
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- When linking to SCSL with -lscs or -lscs_mp, the default integer size is
- 4 bytes (32 bits). Another version of SCSL is available in which integers
- are 8 bytes (64 bits). This version allows the user access to larger
- memory sizes and helps when porting legacy Cray codes. It can be loaded
- by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
- only one of the two versions; 4-byte integer and 8-byte integer library
- calls cannot be mixed.
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- PPPPUUUURRRRPPPPOOOOSSSSEEEE
- DGEQR2 computes a QR factorization of a real m by n matrix A: A = Q * R.
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- M (input) INTEGER
- The number of rows of the matrix A. M >= 0.
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- N (input) INTEGER
- The number of columns of the matrix A. N >= 0.
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- A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
- On entry, the m by n matrix A. On exit, the elements on and
- above the diagonal of the array contain the min(m,n) by n upper
- trapezoidal matrix R (R is upper triangular if m >= n); the
- elements below the diagonal, with the array TAU, represent the
- orthogonal matrix Q as a product of elementary reflectors (see
- Further Details). LDA (input) INTEGER The leading dimension
- of the array A. LDA >= max(1,M).
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- TAU (output) DOUBLE PRECISION array, dimension (min(M,N))
- The scalar factors of the elementary reflectors (see Further
- Details).
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- WORK (workspace) DOUBLE PRECISION array, dimension (N)
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- INFO (output) INTEGER
- = 0: successful exit
- < 0: if INFO = -i, the i-th argument had an illegal value
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- The matrix Q is represented as a product of elementary reflectors
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- Q = H(1) H(2) . . . H(k), where k = min(m,n).
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- Each H(i) has the form
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- H(i) = I - tau * v * v'
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- where tau is a real scalar, and v is a real vector with
- v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i), and
- tau in TAU(i).
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- INTRO_LAPACK(3S), INTRO_SCSL(3S)
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- This man page is available only online.
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