Mercurial > octave-nkf

comparison libcruft/lapack/sgetf2.f @ 7789:82be108cc558

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
First attempt at single precision tyeps * * * corrections to qrupdate single precision routines * * * prefer demotion to single over promotion to double * * * Add single precision support to log2 function * * * Trivial PROJECT file update * * * Cache optimized hermitian/transpose methods * * * Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author David Bateman <dbateman@free.fr>
date Sun, 27 Apr 2008 22:34:17 +0200
parents
children
comparison
equal deleted inserted replaced
7788:45f5faba05a2 7789:82be108cc558
1 SUBROUTINE SGETF2( M, N, A, LDA, IPIV, INFO )
2 *
3 * -- LAPACK routine (version 3.1) --
4 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
5 * November 2006
6 *
7 * .. Scalar Arguments ..
8 INTEGER INFO, LDA, M, N
9 * ..
10 * .. Array Arguments ..
11 INTEGER IPIV( * )
12 REAL A( LDA, * )
13 * ..
14 *
15 * Purpose
16 * =======
17 *
18 * SGETF2 computes an LU factorization of a general m-by-n matrix A
19 * using partial pivoting with row interchanges.
20 *
21 * The factorization has the form
22 * A = P * L * U
23 * where P is a permutation matrix, L is lower triangular with unit
24 * diagonal elements (lower trapezoidal if m > n), and U is upper
25 * triangular (upper trapezoidal if m < n).
26 *
27 * This is the right-looking Level 2 BLAS version of the algorithm.
28 *
29 * Arguments
30 * =========
31 *
32 * M (input) INTEGER
33 * The number of rows of the matrix A. M >= 0.
34 *
35 * N (input) INTEGER
36 * The number of columns of the matrix A. N >= 0.
37 *
38 * A (input/output) REAL array, dimension (LDA,N)
39 * On entry, the m by n matrix to be factored.
40 * On exit, the factors L and U from the factorization
41 * A = P*L*U; the unit diagonal elements of L are not stored.
42 *
43 * LDA (input) INTEGER
44 * The leading dimension of the array A. LDA >= max(1,M).
45 *
46 * IPIV (output) INTEGER array, dimension (min(M,N))
47 * The pivot indices; for 1 <= i <= min(M,N), row i of the
48 * matrix was interchanged with row IPIV(i).
49 *
50 * INFO (output) INTEGER
51 * = 0: successful exit
52 * < 0: if INFO = -k, the k-th argument had an illegal value
53 * > 0: if INFO = k, U(k,k) is exactly zero. The factorization
54 * has been completed, but the factor U is exactly
55 * singular, and division by zero will occur if it is used
56 * to solve a system of equations.
57 *
58 * =====================================================================
59 *
60 * .. Parameters ..
61 REAL ONE, ZERO
62 PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
63 * ..
64 * .. Local Scalars ..
65 REAL SFMIN
66 INTEGER I, J, JP
67 * ..
68 * .. External Functions ..
69 REAL SLAMCH
70 INTEGER ISAMAX
71 EXTERNAL SLAMCH, ISAMAX
72 * ..
73 * .. External Subroutines ..
74 EXTERNAL SGER, SSCAL, SSWAP, XERBLA
75 * ..
76 * .. Intrinsic Functions ..
77 INTRINSIC MAX, MIN
78 * ..
79 * .. Executable Statements ..
80 *
81 * Test the input parameters.
82 *
83 INFO = 0
84 IF( M.LT.0 ) THEN
85 INFO = -1
86 ELSE IF( N.LT.0 ) THEN
87 INFO = -2
88 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
89 INFO = -4
90 END IF
91 IF( INFO.NE.0 ) THEN
92 CALL XERBLA( 'SGETF2', -INFO )
93 RETURN
94 END IF
95 *
96 * Quick return if possible
97 *
98 IF( M.EQ.0 .OR. N.EQ.0 )
99 $ RETURN
100 *
101 * Compute machine safe minimum
102 *
103 SFMIN = SLAMCH('S')
104 *
105 DO 10 J = 1, MIN( M, N )
106 *
107 * Find pivot and test for singularity.
108 *
109 JP = J - 1 + ISAMAX( M-J+1, A( J, J ), 1 )
110 IPIV( J ) = JP
111 IF( A( JP, J ).NE.ZERO ) THEN
112 *
113 * Apply the interchange to columns 1:N.
114 *
115 IF( JP.NE.J )
116 $ CALL SSWAP( N, A( J, 1 ), LDA, A( JP, 1 ), LDA )
117 *
118 * Compute elements J+1:M of J-th column.
119 *
120 IF( J.LT.M ) THEN
121 IF( ABS(A( J, J )) .GE. SFMIN ) THEN
122 CALL SSCAL( M-J, ONE / A( J, J ), A( J+1, J ), 1 )
123 ELSE
124 DO 20 I = 1, M-J
125 A( J+I, J ) = A( J+I, J ) / A( J, J )
126 20 CONTINUE
127 END IF
128 END IF
129 *
130 ELSE IF( INFO.EQ.0 ) THEN
131 *
132 INFO = J
133 END IF
134 *
135 IF( J.LT.MIN( M, N ) ) THEN
136 *
137 * Update trailing submatrix.
138 *
139 CALL SGER( M-J, N-J, -ONE, A( J+1, J ), 1, A( J, J+1 ), LDA,
140 $ A( J+1, J+1 ), LDA )
141 END IF
142 10 CONTINUE
143 RETURN
144 *
145 * End of SGETF2
146 *
147 END