LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine sgetrf ( integer  M,
integer  N,
real, dimension( lda, * )  A,
integer  LDA,
integer, dimension( * )  IPIV,
integer  INFO 
)

SGETRF VARIANT: left-looking Level 3 BLAS version of the algorithm.

Purpose: 

 SGETRF computes an LU factorization of a general M-by-N matrix A
 using partial pivoting with row interchanges.

 The factorization has the form
    A = P * L * U
 where P is a permutation matrix, L is lower triangular with unit
 diagonal elements (lower trapezoidal if m > n), and U is upper
 triangular (upper trapezoidal if m < n).

 This is the left-looking Level 3 BLAS version of the algorithm.
Parameters
[in]M
          M is INTEGER
          The number of rows of the matrix A.  M >= 0.
[in]N
          N is INTEGER
          The number of columns of the matrix A.  N >= 0.
[in,out]A
          A is REAL array, dimension (LDA,N)
          On entry, the M-by-N matrix to be factored.
          On exit, the factors L and U from the factorization
          A = P*L*U; the unit diagonal elements of L are not stored.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,M).
[out]IPIV
          IPIV is INTEGER array, dimension (min(M,N))
          The pivot indices; for 1 <= i <= min(M,N), row i of the
          matrix was interchanged with row IPIV(i).
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  if INFO = i, U(i,i) is exactly zero. The factorization
                has been completed, but the factor U is exactly
                singular, and division by zero will occur if it is used
                to solve a system of equations.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 102 of file sgetrf.f.

102 *
103 * -- LAPACK computational routine (version 3.1) --
104 * -- LAPACK is a software package provided by Univ. of Tennessee, --
105 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
106 * November 2011
107 *
108 * .. Scalar Arguments ..
109  INTEGER info, lda, m, n
110 * ..
111 * .. Array Arguments ..
112  INTEGER ipiv( * )
113  REAL a( lda, * )
114 * ..
115 *
116 * =====================================================================
117 *
118 * .. Parameters ..
119  REAL one
120  parameter ( one = 1.0e+0 )
121 * ..
122 * .. Local Scalars ..
123  INTEGER i, iinfo, j, jb, k, nb
124 * ..
125 * .. External Subroutines ..
126  EXTERNAL sgemm, sgetf2, slaswp, strsm, xerbla
127 * ..
128 * .. External Functions ..
129  INTEGER ilaenv
130  EXTERNAL ilaenv
131 * ..
132 * .. Intrinsic Functions ..
133  INTRINSIC max, min
134 * ..
135 * .. Executable Statements ..
136 *
137 * Test the input parameters.
138 *
139  info = 0
140  IF( m.LT.0 ) THEN
141  info = -1
142  ELSE IF( n.LT.0 ) THEN
143  info = -2
144  ELSE IF( lda.LT.max( 1, m ) ) THEN
145  info = -4
146  END IF
147  IF( info.NE.0 ) THEN
148  CALL xerbla( 'SGETRF', -info )
149  RETURN
150  END IF
151 *
152 * Quick return if possible
153 *
154  IF( m.EQ.0 .OR. n.EQ.0 )
155  $ RETURN
156 *
157 * Determine the block size for this environment.
158 *
159  nb = ilaenv( 1, 'SGETRF', ' ', m, n, -1, -1 )
160  IF( nb.LE.1 .OR. nb.GE.min( m, n ) ) THEN
161 *
162 * Use unblocked code.
163 *
164  CALL sgetf2( m, n, a, lda, ipiv, info )
165 
166  ELSE
167 *
168 * Use blocked code.
169 *
170  DO 20 j = 1, min( m, n ), nb
171  jb = min( min( m, n )-j+1, nb )
172 *
173 *
174 * Update before factoring the current panel
175 *
176  DO 30 k = 1, j-nb, nb
177 *
178 * Apply interchanges to rows K:K+NB-1.
179 *
180  CALL slaswp( jb, a(1, j), lda, k, k+nb-1, ipiv, 1 )
181 *
182 * Compute block row of U.
183 *
184  CALL strsm( 'Left', 'Lower', 'No transpose', 'Unit',
185  $ nb, jb, one, a( k, k ), lda,
186  $ a( k, j ), lda )
187 *
188 * Update trailing submatrix.
189 *
190  CALL sgemm( 'No transpose', 'No transpose',
191  $ m-k-nb+1, jb, nb, -one,
192  $ a( k+nb, k ), lda, a( k, j ), lda, one,
193  $ a( k+nb, j ), lda )
194  30 CONTINUE
195 *
196 * Factor diagonal and subdiagonal blocks and test for exact
197 * singularity.
198 *
199  CALL sgetf2( m-j+1, jb, a( j, j ), lda, ipiv( j ), iinfo )
200 *
201 * Adjust INFO and the pivot indices.
202 *
203  IF( info.EQ.0 .AND. iinfo.GT.0 )
204  $ info = iinfo + j - 1
205  DO 10 i = j, min( m, j+jb-1 )
206  ipiv( i ) = j - 1 + ipiv( i )
207  10 CONTINUE
208 *
209  20 CONTINUE
210 
211 *
212 * Apply interchanges to the left-overs
213 *
214  DO 40 k = 1, min( m, n ), nb
215  CALL slaswp( k-1, a( 1, 1 ), lda, k,
216  $ min(k+nb-1, min( m, n )), ipiv, 1 )
217  40 CONTINUE
218 *
219 * Apply update to the M+1:N columns when N > M
220 *
221  IF ( n.GT.m ) THEN
222 
223  CALL slaswp( n-m, a(1, m+1), lda, 1, m, ipiv, 1 )
224 
225  DO 50 k = 1, m, nb
226 
227  jb = min( m-k+1, nb )
228 *
229  CALL strsm( 'Left', 'Lower', 'No transpose', 'Unit',
230  $ jb, n-m, one, a( k, k ), lda,
231  $ a( k, m+1 ), lda )
232 
233 *
234  IF ( k+nb.LE.m ) THEN
235  CALL sgemm( 'No transpose', 'No transpose',
236  $ m-k-nb+1, n-m, nb, -one,
237  $ a( k+nb, k ), lda, a( k, m+1 ), lda, one,
238  $ a( k+nb, m+1 ), lda )
239  END IF
240  50 CONTINUE
241  END IF
242 *
243  END IF
244  RETURN
245 *
246 * End of SGETRF
247 *
strsm
subroutine strsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
STRSM
Definition: strsm.f:183
sgetf2
subroutine sgetf2(M, N, A, LDA, IPIV, INFO)
SGETF2 computes the LU factorization of a general m-by-n matrix using partial pivoting with row inter...
Definition: sgetf2.f:110
sgemm
subroutine sgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
SGEMM
Definition: sgemm.f:189
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
slaswp
subroutine slaswp(N, A, LDA, K1, K2, IPIV, INCX)
SLASWP performs a series of row interchanges on a general rectangular matrix.
Definition: slaswp.f:116
ilaenv
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
Definition: tstiee.f:83

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