Annotation of rpl/lapack/lapack/zgttrs.f, revision 1.18
1.8 bertrand 1: *> \brief \b ZGTTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
1.15 bertrand 5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
1.8 bertrand 7: *
8: *> \htmlonly
1.15 bertrand 9: *> Download ZGTTRS + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zgttrs.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zgttrs.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zgttrs.f">
1.8 bertrand 15: *> [TXT]</a>
1.15 bertrand 16: *> \endhtmlonly
1.8 bertrand 17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE ZGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB,
22: * INFO )
1.15 bertrand 23: *
1.8 bertrand 24: * .. Scalar Arguments ..
25: * CHARACTER TRANS
26: * INTEGER INFO, LDB, N, NRHS
27: * ..
28: * .. Array Arguments ..
29: * INTEGER IPIV( * )
30: * COMPLEX*16 B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
31: * ..
1.15 bertrand 32: *
1.8 bertrand 33: *
34: *> \par Purpose:
35: * =============
36: *>
37: *> \verbatim
38: *>
39: *> ZGTTRS solves one of the systems of equations
40: *> A * X = B, A**T * X = B, or A**H * X = B,
41: *> with a tridiagonal matrix A using the LU factorization computed
42: *> by ZGTTRF.
43: *> \endverbatim
44: *
45: * Arguments:
46: * ==========
47: *
48: *> \param[in] TRANS
49: *> \verbatim
50: *> TRANS is CHARACTER*1
51: *> Specifies the form of the system of equations.
52: *> = 'N': A * X = B (No transpose)
53: *> = 'T': A**T * X = B (Transpose)
54: *> = 'C': A**H * X = B (Conjugate transpose)
55: *> \endverbatim
56: *>
57: *> \param[in] N
58: *> \verbatim
59: *> N is INTEGER
60: *> The order of the matrix A.
61: *> \endverbatim
62: *>
63: *> \param[in] NRHS
64: *> \verbatim
65: *> NRHS is INTEGER
66: *> The number of right hand sides, i.e., the number of columns
67: *> of the matrix B. NRHS >= 0.
68: *> \endverbatim
69: *>
70: *> \param[in] DL
71: *> \verbatim
72: *> DL is COMPLEX*16 array, dimension (N-1)
73: *> The (n-1) multipliers that define the matrix L from the
74: *> LU factorization of A.
75: *> \endverbatim
76: *>
77: *> \param[in] D
78: *> \verbatim
79: *> D is COMPLEX*16 array, dimension (N)
80: *> The n diagonal elements of the upper triangular matrix U from
81: *> the LU factorization of A.
82: *> \endverbatim
83: *>
84: *> \param[in] DU
85: *> \verbatim
86: *> DU is COMPLEX*16 array, dimension (N-1)
87: *> The (n-1) elements of the first super-diagonal of U.
88: *> \endverbatim
89: *>
90: *> \param[in] DU2
91: *> \verbatim
92: *> DU2 is COMPLEX*16 array, dimension (N-2)
93: *> The (n-2) elements of the second super-diagonal of U.
94: *> \endverbatim
95: *>
96: *> \param[in] IPIV
97: *> \verbatim
98: *> IPIV is INTEGER array, dimension (N)
99: *> The pivot indices; for 1 <= i <= n, row i of the matrix was
100: *> interchanged with row IPIV(i). IPIV(i) will always be either
101: *> i or i+1; IPIV(i) = i indicates a row interchange was not
102: *> required.
103: *> \endverbatim
104: *>
105: *> \param[in,out] B
106: *> \verbatim
107: *> B is COMPLEX*16 array, dimension (LDB,NRHS)
108: *> On entry, the matrix of right hand side vectors B.
109: *> On exit, B is overwritten by the solution vectors X.
110: *> \endverbatim
111: *>
112: *> \param[in] LDB
113: *> \verbatim
114: *> LDB is INTEGER
115: *> The leading dimension of the array B. LDB >= max(1,N).
116: *> \endverbatim
117: *>
118: *> \param[out] INFO
119: *> \verbatim
120: *> INFO is INTEGER
121: *> = 0: successful exit
122: *> < 0: if INFO = -k, the k-th argument had an illegal value
123: *> \endverbatim
124: *
125: * Authors:
126: * ========
127: *
1.15 bertrand 128: *> \author Univ. of Tennessee
129: *> \author Univ. of California Berkeley
130: *> \author Univ. of Colorado Denver
131: *> \author NAG Ltd.
1.8 bertrand 132: *
1.11 bertrand 133: *> \ingroup complex16GTcomputational
1.8 bertrand 134: *
135: * =====================================================================
1.1 bertrand 136: SUBROUTINE ZGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB,
137: $ INFO )
138: *
1.18 ! bertrand 139: * -- LAPACK computational routine --
1.1 bertrand 140: * -- LAPACK is a software package provided by Univ. of Tennessee, --
141: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
142: *
143: * .. Scalar Arguments ..
144: CHARACTER TRANS
145: INTEGER INFO, LDB, N, NRHS
146: * ..
147: * .. Array Arguments ..
148: INTEGER IPIV( * )
149: COMPLEX*16 B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
150: * ..
151: *
152: * =====================================================================
153: *
154: * .. Local Scalars ..
155: LOGICAL NOTRAN
156: INTEGER ITRANS, J, JB, NB
157: * ..
158: * .. External Functions ..
159: INTEGER ILAENV
160: EXTERNAL ILAENV
161: * ..
162: * .. External Subroutines ..
163: EXTERNAL XERBLA, ZGTTS2
164: * ..
165: * .. Intrinsic Functions ..
166: INTRINSIC MAX, MIN
167: * ..
168: * .. Executable Statements ..
169: *
170: INFO = 0
171: NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' )
172: IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ.
173: $ 't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN
174: INFO = -1
175: ELSE IF( N.LT.0 ) THEN
176: INFO = -2
177: ELSE IF( NRHS.LT.0 ) THEN
178: INFO = -3
179: ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN
180: INFO = -10
181: END IF
182: IF( INFO.NE.0 ) THEN
183: CALL XERBLA( 'ZGTTRS', -INFO )
184: RETURN
185: END IF
186: *
187: * Quick return if possible
188: *
189: IF( N.EQ.0 .OR. NRHS.EQ.0 )
190: $ RETURN
191: *
192: * Decode TRANS
193: *
194: IF( NOTRAN ) THEN
195: ITRANS = 0
196: ELSE IF( TRANS.EQ.'T' .OR. TRANS.EQ.'t' ) THEN
197: ITRANS = 1
198: ELSE
199: ITRANS = 2
200: END IF
201: *
202: * Determine the number of right-hand sides to solve at a time.
203: *
204: IF( NRHS.EQ.1 ) THEN
205: NB = 1
206: ELSE
207: NB = MAX( 1, ILAENV( 1, 'ZGTTRS', TRANS, N, NRHS, -1, -1 ) )
208: END IF
209: *
210: IF( NB.GE.NRHS ) THEN
211: CALL ZGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB )
212: ELSE
213: DO 10 J = 1, NRHS, NB
214: JB = MIN( NRHS-J+1, NB )
215: CALL ZGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ),
216: $ LDB )
217: 10 CONTINUE
218: END IF
219: *
220: * End of ZGTTRS
221: *
222: END
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