1*> \brief \b CGETRS
2*
3*  =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6*            http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
9*> Download CGETRS + dependencies
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/cgetrs.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/cgetrs.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/cgetrs.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18*  Definition:
19*  ===========
20*
21*       SUBROUTINE CGETRS( 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*       COMPLEX            A( LDA, * ), B( LDB, * )
30*       ..
31*
32*
33*> \par Purpose:
34*  =============
35*>
36*> \verbatim
37*>
38*> CGETRS solves a system of linear equations
39*>    A * X = B,  A**T * X = B,  or  A**H * X = B
40*> with a general N-by-N matrix A using the LU factorization computed
41*> by CGETRF.
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**H * X = B  (Conjugate 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 COMPLEX array, dimension (LDA,N)
72*>          The factors L and U from the factorization A = P*L*U
73*>          as computed by CGETRF.
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 CGETRF; 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 COMPLEX 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*> \ingroup complexGEcomputational
118*
119*  =====================================================================
120      SUBROUTINE CGETRS( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO )
121*
122*  -- LAPACK computational routine --
123*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
124*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
125*
126*     .. Scalar Arguments ..
127      CHARACTER          TRANS
128      INTEGER            INFO, LDA, LDB, N, NRHS
129*     ..
130*     .. Array Arguments ..
131      INTEGER            IPIV( * )
132      COMPLEX            A( LDA, * ), B( LDB, * )
133*     ..
134*
135*  =====================================================================
136*
137*     .. Parameters ..
138      COMPLEX            ONE
139      PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ) )
140*     ..
141*     .. Local Scalars ..
142      LOGICAL            NOTRAN
143*     ..
144*     .. External Functions ..
145      LOGICAL            LSAME
146      EXTERNAL           LSAME
147*     ..
148*     .. External Subroutines ..
149      EXTERNAL           CLASWP, CTRSM, XERBLA
150*     ..
151*     .. Intrinsic Functions ..
152      INTRINSIC          MAX
153*     ..
154*     .. Executable Statements ..
155*
156*     Test the input parameters.
157*
158      INFO = 0
159      NOTRAN = LSAME( TRANS, 'N' )
160      IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) .AND. .NOT.
161     $    LSAME( TRANS, 'C' ) ) THEN
162         INFO = -1
163      ELSE IF( N.LT.0 ) THEN
164         INFO = -2
165      ELSE IF( NRHS.LT.0 ) THEN
166         INFO = -3
167      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
168         INFO = -5
169      ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
170         INFO = -8
171      END IF
172      IF( INFO.NE.0 ) THEN
173         CALL XERBLA( 'CGETRS', -INFO )
174         RETURN
175      END IF
176*
177*     Quick return if possible
178*
179      IF( N.EQ.0 .OR. NRHS.EQ.0 )
180     $   RETURN
181*
182      IF( NOTRAN ) THEN
183*
184*        Solve A * X = B.
185*
186*        Apply row interchanges to the right hand sides.
187*
188         CALL CLASWP( NRHS, B, LDB, 1, N, IPIV, 1 )
189*
190*        Solve L*X = B, overwriting B with X.
191*
192         CALL CTRSM( 'Left', 'Lower', 'No transpose', 'Unit', N, NRHS,
193     $               ONE, A, LDA, B, LDB )
194*
195*        Solve U*X = B, overwriting B with X.
196*
197         CALL CTRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N,
198     $               NRHS, ONE, A, LDA, B, LDB )
199      ELSE
200*
201*        Solve A**T * X = B  or A**H * X = B.
202*
203*        Solve U**T *X = B or U**H *X = B, overwriting B with X.
204*
205         CALL CTRSM( 'Left', 'Upper', TRANS, 'Non-unit', N, NRHS, ONE,
206     $               A, LDA, B, LDB )
207*
208*        Solve L**T *X = B, or L**H *X = B overwriting B with X.
209*
210         CALL CTRSM( 'Left', 'Lower', TRANS, 'Unit', N, NRHS, ONE, A,
211     $               LDA, B, LDB )
212*
213*        Apply row interchanges to the solution vectors.
214*
215         CALL CLASWP( NRHS, B, LDB, 1, N, IPIV, -1 )
216      END IF
217*
218      RETURN
219*
220*     End of CGETRS
221*
222      END
223