Annotation of rpl/lapack/lapack/dgttrs.f, revision 1.15
1.9 bertrand 1: *> \brief \b DGTTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download DGTTRS + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dgttrs.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dgttrs.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dgttrs.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB,
22: * INFO )
23: *
24: * .. Scalar Arguments ..
25: * CHARACTER TRANS
26: * INTEGER INFO, LDB, N, NRHS
27: * ..
28: * .. Array Arguments ..
29: * INTEGER IPIV( * )
30: * DOUBLE PRECISION B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
31: * ..
32: *
33: *
34: *> \par Purpose:
35: * =============
36: *>
37: *> \verbatim
38: *>
39: *> DGTTRS solves one of the systems of equations
40: *> A*X = B or A**T*X = B,
41: *> with a tridiagonal matrix A using the LU factorization computed
42: *> by DGTTRF.
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**T* X = B (Conjugate transpose = 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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 = -i, the i-th argument had an illegal value
123: *> \endverbatim
124: *
125: * Authors:
126: * ========
127: *
128: *> \author Univ. of Tennessee
129: *> \author Univ. of California Berkeley
130: *> \author Univ. of Colorado Denver
131: *> \author NAG Ltd.
132: *
1.12 bertrand 133: *> \date September 2012
1.9 bertrand 134: *
1.12 bertrand 135: *> \ingroup doubleGTcomputational
1.9 bertrand 136: *
137: * =====================================================================
1.1 bertrand 138: SUBROUTINE DGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB,
139: $ INFO )
140: *
1.12 bertrand 141: * -- LAPACK computational routine (version 3.4.2) --
1.1 bertrand 142: * -- LAPACK is a software package provided by Univ. of Tennessee, --
143: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.12 bertrand 144: * September 2012
1.1 bertrand 145: *
146: * .. Scalar Arguments ..
147: CHARACTER TRANS
148: INTEGER INFO, LDB, N, NRHS
149: * ..
150: * .. Array Arguments ..
151: INTEGER IPIV( * )
152: DOUBLE PRECISION B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
153: * ..
154: *
155: * =====================================================================
156: *
157: * .. Local Scalars ..
158: LOGICAL NOTRAN
159: INTEGER ITRANS, J, JB, NB
160: * ..
161: * .. External Functions ..
162: INTEGER ILAENV
163: EXTERNAL ILAENV
164: * ..
165: * .. External Subroutines ..
166: EXTERNAL DGTTS2, XERBLA
167: * ..
168: * .. Intrinsic Functions ..
169: INTRINSIC MAX, MIN
170: * ..
171: * .. Executable Statements ..
172: *
173: INFO = 0
174: NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' )
175: IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ.
176: $ 't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN
177: INFO = -1
178: ELSE IF( N.LT.0 ) THEN
179: INFO = -2
180: ELSE IF( NRHS.LT.0 ) THEN
181: INFO = -3
182: ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN
183: INFO = -10
184: END IF
185: IF( INFO.NE.0 ) THEN
186: CALL XERBLA( 'DGTTRS', -INFO )
187: RETURN
188: END IF
189: *
190: * Quick return if possible
191: *
192: IF( N.EQ.0 .OR. NRHS.EQ.0 )
193: $ RETURN
194: *
195: * Decode TRANS
196: *
197: IF( NOTRAN ) THEN
198: ITRANS = 0
199: ELSE
200: ITRANS = 1
201: END IF
202: *
203: * Determine the number of right-hand sides to solve at a time.
204: *
205: IF( NRHS.EQ.1 ) THEN
206: NB = 1
207: ELSE
208: NB = MAX( 1, ILAENV( 1, 'DGTTRS', TRANS, N, NRHS, -1, -1 ) )
209: END IF
210: *
211: IF( NB.GE.NRHS ) THEN
212: CALL DGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB )
213: ELSE
214: DO 10 J = 1, NRHS, NB
215: JB = MIN( NRHS-J+1, NB )
216: CALL DGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ),
217: $ LDB )
218: 10 CONTINUE
219: END IF
220: *
221: * End of DGTTRS
222: *
223: END
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