1 SUBROUTINE SGETF2F( M, N, A, LDA, IPIV, INFO )
3 * -- LAPACK routine (version 3.0) --
4 * Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
5 * Courant Institute, Argonne National Lab, and Rice University
8 * .. Scalar Arguments ..
9 INTEGER INFO, LDA, M, N
11 * .. Array Arguments ..
19 * SGETF2 computes an LU factorization of a general m-by-n matrix A
20 * using partial pivoting with row interchanges.
22 * The factorization has the form
24 * where P is a permutation matrix, L is lower triangular with unit
25 * diagonal elements (lower trapezoidal if m > n), and U is upper
26 * triangular (upper trapezoidal if m < n).
28 * This is the right-looking Level 2 BLAS version of the algorithm.
34 * The number of rows of the matrix A. M >= 0.
37 * The number of columns of the matrix A. N >= 0.
39 * A (input/output) REAL array, dimension (LDA,N)
40 * On entry, the m by n matrix to be factored.
41 * On exit, the factors L and U from the factorization
42 * A = P*L*U; the unit diagonal elements of L are not stored.
45 * The leading dimension of the array A. LDA >= max(1,M).
47 * IPIV (output) INTEGER array, dimension (min(M,N))
48 * The pivot indices; for 1 <= i <= min(M,N), row i of the
49 * matrix was interchanged with row IPIV(i).
51 * INFO (output) INTEGER
52 * = 0: successful exit
53 * < 0: if INFO = -k, the k-th argument had an illegal value
54 * > 0: if INFO = k, U(k,k) is exactly zero. The factorization
55 * has been completed, but the factor U is exactly
56 * singular, and division by zero will occur if it is used
57 * to solve a system of equations.
59 * =====================================================================
63 PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
68 * .. External Functions ..
72 * .. External Subroutines ..
73 EXTERNAL SGER, SSCAL, SSWAP, XERBLA
75 * .. Intrinsic Functions ..
78 * .. Executable Statements ..
80 * Test the input parameters.
85 ELSE IF( N.LT.0 ) THEN
87 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
91 CALL XERBLA( 'SGETF2', -INFO )
95 * Quick return if possible
97 IF( M.EQ.0 .OR. N.EQ.0 )
100 DO 10 J = 1, MIN( M, N )
102 * Find pivot and test for singularity.
104 JP = J - 1 + ISAMAX( M-J+1, A( J, J ), 1 )
106 IF( A( JP, J ).NE.ZERO ) THEN
108 * Apply the interchange to columns 1:N.
111 $ CALL SSWAP( N, A( J, 1 ), LDA, A( JP, 1 ), LDA )
113 * Compute elements J+1:M of J-th column.
116 $ CALL SSCAL( M-J, ONE / A( J, J ), A( J+1, J ), 1 )
118 ELSE IF( INFO.EQ.0 ) THEN
123 IF( J.LT.MIN( M, N ) ) THEN
125 * Update trailing submatrix.
127 CALL SGER( M-J, N-J, -ONE, A( J+1, J ), 1, A( J, J+1 ), LDA,
128 $ A( J+1, J+1 ), LDA )