Mercurial > octave-nkf
diff libcruft/lapack/sgeqr2.f @ 7789:82be108cc558
First attempt at single precision tyeps
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corrections to qrupdate single precision routines
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prefer demotion to single over promotion to double
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Add single precision support to log2 function
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Trivial PROJECT file update
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Cache optimized hermitian/transpose methods
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Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author | David Bateman <dbateman@free.fr> |
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date | Sun, 27 Apr 2008 22:34:17 +0200 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/libcruft/lapack/sgeqr2.f Sun Apr 27 22:34:17 2008 +0200 @@ -0,0 +1,121 @@ + SUBROUTINE SGEQR2( M, N, A, LDA, TAU, WORK, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER INFO, LDA, M, N +* .. +* .. Array Arguments .. + REAL A( LDA, * ), TAU( * ), WORK( * ) +* .. +* +* Purpose +* ======= +* +* SGEQR2 computes a QR factorization of a real m by n matrix A: +* A = Q * R. +* +* Arguments +* ========= +* +* M (input) INTEGER +* The number of rows of the matrix A. M >= 0. +* +* N (input) INTEGER +* The number of columns of the matrix A. N >= 0. +* +* A (input/output) REAL 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). +* +* TAU (output) REAL array, dimension (min(M,N)) +* The scalar factors of the elementary reflectors (see Further +* Details). +* +* WORK (workspace) REAL array, dimension (N) +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -i, the i-th argument had an illegal value +* +* Further Details +* =============== +* +* The matrix Q is represented as a product of elementary reflectors +* +* Q = H(1) H(2) . . . H(k), where k = min(m,n). +* +* Each H(i) has the form +* +* H(i) = I - tau * v * v' +* +* 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). +* +* ===================================================================== +* +* .. Parameters .. + REAL ONE + PARAMETER ( ONE = 1.0E+0 ) +* .. +* .. Local Scalars .. + INTEGER I, K + REAL AII +* .. +* .. External Subroutines .. + EXTERNAL SLARF, SLARFG, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, MIN +* .. +* .. Executable Statements .. +* +* Test the input arguments +* + INFO = 0 + IF( M.LT.0 ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( LDA.LT.MAX( 1, M ) ) THEN + INFO = -4 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'SGEQR2', -INFO ) + RETURN + END IF +* + K = MIN( M, N ) +* + DO 10 I = 1, K +* +* Generate elementary reflector H(i) to annihilate A(i+1:m,i) +* + CALL SLARFG( M-I+1, A( I, I ), A( MIN( I+1, M ), I ), 1, + $ TAU( I ) ) + IF( I.LT.N ) THEN +* +* Apply H(i) to A(i:m,i+1:n) from the left +* + AII = A( I, I ) + A( I, I ) = ONE + CALL SLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ), + $ A( I, I+1 ), LDA, WORK ) + A( I, I ) = AII + END IF + 10 CONTINUE + RETURN +* +* End of SGEQR2 +* + END