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sgetrs.f
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1 *> \brief \b SGETRS
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 *> \htmlonly
9 *> Download SGETRS + dependencies
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11 *> [TGZ]</a>
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13 *> [ZIP]</a>
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/sgetrs.f">
15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE SGETRS( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER TRANS
25 * INTEGER INFO, LDA, LDB, N, NRHS
26 * ..
27 * .. Array Arguments ..
28 * INTEGER IPIV( * )
29 * REAL A( LDA, * ), B( LDB, * )
30 * ..
31 *
32 *
33 *> \par Purpose:
34 * =============
35 *>
36 *> \verbatim
37 *>
38 *> SGETRS solves a system of linear equations
39 *> A * X = B or A**T * X = B
40 *> with a general N-by-N matrix A using the LU factorization computed
41 *> by SGETRF.
42 *> \endverbatim
43 *
44 * Arguments:
45 * ==========
46 *
47 *> \param[in] TRANS
48 *> \verbatim
49 *> TRANS is CHARACTER*1
50 *> Specifies the form of the system of equations:
51 *> = 'N': A * X = B (No transpose)
52 *> = 'T': A**T* X = B (Transpose)
53 *> = 'C': A**T* X = B (Conjugate transpose = Transpose)
54 *> \endverbatim
55 *>
56 *> \param[in] N
57 *> \verbatim
58 *> N is INTEGER
59 *> The order of the matrix A. N >= 0.
60 *> \endverbatim
61 *>
62 *> \param[in] NRHS
63 *> \verbatim
64 *> NRHS is INTEGER
65 *> The number of right hand sides, i.e., the number of columns
66 *> of the matrix B. NRHS >= 0.
67 *> \endverbatim
68 *>
69 *> \param[in] A
70 *> \verbatim
71 *> A is REAL array, dimension (LDA,N)
72 *> The factors L and U from the factorization A = P*L*U
73 *> as computed by SGETRF.
74 *> \endverbatim
75 *>
76 *> \param[in] LDA
77 *> \verbatim
78 *> LDA is INTEGER
79 *> The leading dimension of the array A. LDA >= max(1,N).
80 *> \endverbatim
81 *>
82 *> \param[in] IPIV
83 *> \verbatim
84 *> IPIV is INTEGER array, dimension (N)
85 *> The pivot indices from SGETRF; for 1<=i<=N, row i of the
86 *> matrix was interchanged with row IPIV(i).
87 *> \endverbatim
88 *>
89 *> \param[in,out] B
90 *> \verbatim
91 *> B is REAL array, dimension (LDB,NRHS)
92 *> On entry, the right hand side matrix B.
93 *> On exit, the solution matrix X.
94 *> \endverbatim
95 *>
96 *> \param[in] LDB
97 *> \verbatim
98 *> LDB is INTEGER
99 *> The leading dimension of the array B. LDB >= max(1,N).
100 *> \endverbatim
101 *>
102 *> \param[out] INFO
103 *> \verbatim
104 *> INFO is INTEGER
105 *> = 0: successful exit
106 *> < 0: if INFO = -i, the i-th argument had an illegal value
107 *> \endverbatim
108 *
109 * Authors:
110 * ========
111 *
112 *> \author Univ. of Tennessee
113 *> \author Univ. of California Berkeley
114 *> \author Univ. of Colorado Denver
115 *> \author NAG Ltd.
116 *
117 *> \date November 2011
118 *
119 *> \ingroup realGEcomputational
120 *
121 * =====================================================================
122  SUBROUTINE sgetrs( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO )
123 *
124 * -- LAPACK computational routine (version 3.4.0) --
125 * -- LAPACK is a software package provided by Univ. of Tennessee, --
126 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
127 * November 2011
128 *
129 * .. Scalar Arguments ..
130  CHARACTER trans
131  INTEGER info, lda, ldb, n, nrhs
132 * ..
133 * .. Array Arguments ..
134  INTEGER ipiv( * )
135  REAL a( lda, * ), b( ldb, * )
136 * ..
137 *
138 * =====================================================================
139 *
140 * .. Parameters ..
141  REAL one
142  parameter( one = 1.0e+0 )
143 * ..
144 * .. Local Scalars ..
145  LOGICAL notran
146 * ..
147 * .. External Functions ..
148  LOGICAL lsame
149  EXTERNAL lsame
150 * ..
151 * .. External Subroutines ..
152  EXTERNAL slaswp, strsm, xerbla
153 * ..
154 * .. Intrinsic Functions ..
155  INTRINSIC max
156 * ..
157 * .. Executable Statements ..
158 *
159 * Test the input parameters.
160 *
161  info = 0
162  notran = lsame( trans, 'N' )
163  IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) .AND. .NOT.
164  $ lsame( trans, 'C' ) ) THEN
165  info = -1
166  ELSE IF( n.LT.0 ) THEN
167  info = -2
168  ELSE IF( nrhs.LT.0 ) THEN
169  info = -3
170  ELSE IF( lda.LT.max( 1, n ) ) THEN
171  info = -5
172  ELSE IF( ldb.LT.max( 1, n ) ) THEN
173  info = -8
174  END IF
175  IF( info.NE.0 ) THEN
176  CALL xerbla( 'SGETRS', -info )
177  RETURN
178  END IF
179 *
180 * Quick return if possible
181 *
182  IF( n.EQ.0 .OR. nrhs.EQ.0 )
183  $ RETURN
184 *
185  IF( notran ) THEN
186 *
187 * Solve A * X = B.
188 *
189 * Apply row interchanges to the right hand sides.
190 *
191  CALL slaswp( nrhs, b, ldb, 1, n, ipiv, 1 )
192 *
193 * Solve L*X = B, overwriting B with X.
194 *
195  CALL strsm( 'Left', 'Lower', 'No transpose', 'Unit', n, nrhs,
196  $ one, a, lda, b, ldb )
197 *
198 * Solve U*X = B, overwriting B with X.
199 *
200  CALL strsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
201  $ nrhs, one, a, lda, b, ldb )
202  ELSE
203 *
204 * Solve A**T * X = B.
205 *
206 * Solve U**T *X = B, overwriting B with X.
207 *
208  CALL strsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
209  $ one, a, lda, b, ldb )
210 *
211 * Solve L**T *X = B, overwriting B with X.
212 *
213  CALL strsm( 'Left', 'Lower', 'Transpose', 'Unit', n, nrhs, one,
214  $ a, lda, b, ldb )
215 *
216 * Apply row interchanges to the solution vectors.
217 *
218  CALL slaswp( nrhs, b, ldb, 1, n, ipiv, -1 )
219  END IF
220 *
221  RETURN
222 *
223 * End of SGETRS
224 *
225  END