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spotrf.f
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1 *> \brief \b SPOTRF
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 *> \htmlonly
9 *> Download SPOTRF + dependencies
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11 *> [TGZ]</a>
12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/spotrf.f">
13 *> [ZIP]</a>
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/spotrf.f">
15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE SPOTRF( UPLO, N, A, LDA, INFO )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER UPLO
25 * INTEGER INFO, LDA, N
26 * ..
27 * .. Array Arguments ..
28 * REAL A( LDA, * )
29 * ..
30 *
31 *
32 *> \par Purpose:
33 * =============
34 *>
35 *> \verbatim
36 *>
37 *> SPOTRF computes the Cholesky factorization of a real symmetric
38 *> positive definite matrix A.
39 *>
40 *> The factorization has the form
41 *> A = U**T * U, if UPLO = 'U', or
42 *> A = L * L**T, if UPLO = 'L',
43 *> where U is an upper triangular matrix and L is lower triangular.
44 *>
45 *> This is the block version of the algorithm, calling Level 3 BLAS.
46 *> \endverbatim
47 *
48 * Arguments:
49 * ==========
50 *
51 *> \param[in] UPLO
52 *> \verbatim
53 *> UPLO is CHARACTER*1
54 *> = 'U': Upper triangle of A is stored;
55 *> = 'L': Lower triangle of A is stored.
56 *> \endverbatim
57 *>
58 *> \param[in] N
59 *> \verbatim
60 *> N is INTEGER
61 *> The order of the matrix A. N >= 0.
62 *> \endverbatim
63 *>
64 *> \param[in,out] A
65 *> \verbatim
66 *> A is REAL array, dimension (LDA,N)
67 *> On entry, the symmetric matrix A. If UPLO = 'U', the leading
68 *> N-by-N upper triangular part of A contains the upper
69 *> triangular part of the matrix A, and the strictly lower
70 *> triangular part of A is not referenced. If UPLO = 'L', the
71 *> leading N-by-N lower triangular part of A contains the lower
72 *> triangular part of the matrix A, and the strictly upper
73 *> triangular part of A is not referenced.
74 *>
75 *> On exit, if INFO = 0, the factor U or L from the Cholesky
76 *> factorization A = U**T*U or A = L*L**T.
77 *> \endverbatim
78 *>
79 *> \param[in] LDA
80 *> \verbatim
81 *> LDA is INTEGER
82 *> The leading dimension of the array A. LDA >= max(1,N).
83 *> \endverbatim
84 *>
85 *> \param[out] INFO
86 *> \verbatim
87 *> INFO is INTEGER
88 *> = 0: successful exit
89 *> < 0: if INFO = -i, the i-th argument had an illegal value
90 *> > 0: if INFO = i, the leading minor of order i is not
91 *> positive definite, and the factorization could not be
92 *> completed.
93 *> \endverbatim
94 *
95 * Authors:
96 * ========
97 *
98 *> \author Univ. of Tennessee
99 *> \author Univ. of California Berkeley
100 *> \author Univ. of Colorado Denver
101 *> \author NAG Ltd.
102 *
103 *> \date November 2011
104 *
105 *> \ingroup realPOcomputational
106 *
107 * =====================================================================
108  SUBROUTINE spotrf( UPLO, N, A, LDA, INFO )
109 *
110 * -- LAPACK computational routine (version 3.4.0) --
111 * -- LAPACK is a software package provided by Univ. of Tennessee, --
112 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
113 * November 2011
114 *
115 * .. Scalar Arguments ..
116  CHARACTER uplo
117  INTEGER info, lda, n
118 * ..
119 * .. Array Arguments ..
120  REAL a( lda, * )
121 * ..
122 *
123 * =====================================================================
124 *
125 * .. Parameters ..
126  REAL one
127  parameter( one = 1.0e+0 )
128 * ..
129 * .. Local Scalars ..
130  LOGICAL upper
131  INTEGER j, jb, nb
132 * ..
133 * .. External Functions ..
134  LOGICAL lsame
135  INTEGER ilaenv
136  EXTERNAL lsame, ilaenv
137 * ..
138 * .. External Subroutines ..
139  EXTERNAL sgemm, spotf2, ssyrk, strsm, xerbla
140 * ..
141 * .. Intrinsic Functions ..
142  INTRINSIC max, min
143 * ..
144 * .. Executable Statements ..
145 *
146 * Test the input parameters.
147 *
148  info = 0
149  upper = lsame( uplo, 'U' )
150  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
151  info = -1
152  ELSE IF( n.LT.0 ) THEN
153  info = -2
154  ELSE IF( lda.LT.max( 1, n ) ) THEN
155  info = -4
156  END IF
157  IF( info.NE.0 ) THEN
158  CALL xerbla( 'SPOTRF', -info )
159  RETURN
160  END IF
161 *
162 * Quick return if possible
163 *
164  IF( n.EQ.0 )
165  $ RETURN
166 *
167 * Determine the block size for this environment.
168 *
169  nb = ilaenv( 1, 'SPOTRF', uplo, n, -1, -1, -1 )
170  IF( nb.LE.1 .OR. nb.GE.n ) THEN
171 *
172 * Use unblocked code.
173 *
174  CALL spotf2( uplo, n, a, lda, info )
175  ELSE
176 *
177 * Use blocked code.
178 *
179  IF( upper ) THEN
180 *
181 * Compute the Cholesky factorization A = U**T*U.
182 *
183  DO 10 j = 1, n, nb
184 *
185 * Update and factorize the current diagonal block and test
186 * for non-positive-definiteness.
187 *
188  jb = min( nb, n-j+1 )
189  CALL ssyrk( 'Upper', 'Transpose', jb, j-1, -one,
190  $ a( 1, j ), lda, one, a( j, j ), lda )
191  CALL spotf2( 'Upper', jb, a( j, j ), lda, info )
192  IF( info.NE.0 )
193  $ go to 30
194  IF( j+jb.LE.n ) THEN
195 *
196 * Compute the current block row.
197 *
198  CALL sgemm( 'Transpose', 'No transpose', jb, n-j-jb+1,
199  $ j-1, -one, a( 1, j ), lda, a( 1, j+jb ),
200  $ lda, one, a( j, j+jb ), lda )
201  CALL strsm( 'Left', 'Upper', 'Transpose', 'Non-unit',
202  $ jb, n-j-jb+1, one, a( j, j ), lda,
203  $ a( j, j+jb ), lda )
204  END IF
205  10 CONTINUE
206 *
207  ELSE
208 *
209 * Compute the Cholesky factorization A = L*L**T.
210 *
211  DO 20 j = 1, n, nb
212 *
213 * Update and factorize the current diagonal block and test
214 * for non-positive-definiteness.
215 *
216  jb = min( nb, n-j+1 )
217  CALL ssyrk( 'Lower', 'No transpose', jb, j-1, -one,
218  $ a( j, 1 ), lda, one, a( j, j ), lda )
219  CALL spotf2( 'Lower', jb, a( j, j ), lda, info )
220  IF( info.NE.0 )
221  $ go to 30
222  IF( j+jb.LE.n ) THEN
223 *
224 * Compute the current block column.
225 *
226  CALL sgemm( 'No transpose', 'Transpose', n-j-jb+1, jb,
227  $ j-1, -one, a( j+jb, 1 ), lda, a( j, 1 ),
228  $ lda, one, a( j+jb, j ), lda )
229  CALL strsm( 'Right', 'Lower', 'Transpose', 'Non-unit',
230  $ n-j-jb+1, jb, one, a( j, j ), lda,
231  $ a( j+jb, j ), lda )
232  END IF
233  20 CONTINUE
234  END IF
235  END IF
236  go to 40
237 *
238  30 CONTINUE
239  info = info + j - 1
240 *
241  40 CONTINUE
242  RETURN
243 *
244 * End of SPOTRF
245 *
246  END