Annotation of rpl/lapack/lapack/dpttrs.f, revision 1.13
1.9 bertrand 1: *> \brief \b DPTTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download DPTTRS + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dpttrs.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dpttrs.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dpttrs.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
22: *
23: * .. Scalar Arguments ..
24: * INTEGER INFO, LDB, N, NRHS
25: * ..
26: * .. Array Arguments ..
27: * DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
28: * ..
29: *
30: *
31: *> \par Purpose:
32: * =============
33: *>
34: *> \verbatim
35: *>
36: *> DPTTRS solves a tridiagonal system of the form
37: *> A * X = B
38: *> using the L*D*L**T factorization of A computed by DPTTRF. D is a
39: *> diagonal matrix specified in the vector D, L is a unit bidiagonal
40: *> matrix whose subdiagonal is specified in the vector E, and X and B
41: *> are N by NRHS matrices.
42: *> \endverbatim
43: *
44: * Arguments:
45: * ==========
46: *
47: *> \param[in] N
48: *> \verbatim
49: *> N is INTEGER
50: *> The order of the tridiagonal matrix A. N >= 0.
51: *> \endverbatim
52: *>
53: *> \param[in] NRHS
54: *> \verbatim
55: *> NRHS is INTEGER
56: *> The number of right hand sides, i.e., the number of columns
57: *> of the matrix B. NRHS >= 0.
58: *> \endverbatim
59: *>
60: *> \param[in] D
61: *> \verbatim
62: *> D is DOUBLE PRECISION array, dimension (N)
63: *> The n diagonal elements of the diagonal matrix D from the
64: *> L*D*L**T factorization of A.
65: *> \endverbatim
66: *>
67: *> \param[in] E
68: *> \verbatim
69: *> E is DOUBLE PRECISION array, dimension (N-1)
70: *> The (n-1) subdiagonal elements of the unit bidiagonal factor
71: *> L from the L*D*L**T factorization of A. E can also be regarded
72: *> as the superdiagonal of the unit bidiagonal factor U from the
73: *> factorization A = U**T*D*U.
74: *> \endverbatim
75: *>
76: *> \param[in,out] B
77: *> \verbatim
78: *> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
79: *> On entry, the right hand side vectors B for the system of
80: *> linear equations.
81: *> On exit, the solution vectors, X.
82: *> \endverbatim
83: *>
84: *> \param[in] LDB
85: *> \verbatim
86: *> LDB is INTEGER
87: *> The leading dimension of the array B. LDB >= max(1,N).
88: *> \endverbatim
89: *>
90: *> \param[out] INFO
91: *> \verbatim
92: *> INFO is INTEGER
93: *> = 0: successful exit
94: *> < 0: if INFO = -k, the k-th argument had an illegal value
95: *> \endverbatim
96: *
97: * Authors:
98: * ========
99: *
100: *> \author Univ. of Tennessee
101: *> \author Univ. of California Berkeley
102: *> \author Univ. of Colorado Denver
103: *> \author NAG Ltd.
104: *
1.12 bertrand 105: *> \date September 2012
1.9 bertrand 106: *
1.12 bertrand 107: *> \ingroup doublePTcomputational
1.9 bertrand 108: *
109: * =====================================================================
1.1 bertrand 110: SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
111: *
1.12 bertrand 112: * -- LAPACK computational routine (version 3.4.2) --
1.1 bertrand 113: * -- LAPACK is a software package provided by Univ. of Tennessee, --
114: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.12 bertrand 115: * September 2012
1.1 bertrand 116: *
117: * .. Scalar Arguments ..
118: INTEGER INFO, LDB, N, NRHS
119: * ..
120: * .. Array Arguments ..
121: DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
122: * ..
123: *
124: * =====================================================================
125: *
126: * .. Local Scalars ..
127: INTEGER J, JB, NB
128: * ..
129: * .. External Functions ..
130: INTEGER ILAENV
131: EXTERNAL ILAENV
132: * ..
133: * .. External Subroutines ..
134: EXTERNAL DPTTS2, XERBLA
135: * ..
136: * .. Intrinsic Functions ..
137: INTRINSIC MAX, MIN
138: * ..
139: * .. Executable Statements ..
140: *
141: * Test the input arguments.
142: *
143: INFO = 0
144: IF( N.LT.0 ) THEN
145: INFO = -1
146: ELSE IF( NRHS.LT.0 ) THEN
147: INFO = -2
148: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
149: INFO = -6
150: END IF
151: IF( INFO.NE.0 ) THEN
152: CALL XERBLA( 'DPTTRS', -INFO )
153: RETURN
154: END IF
155: *
156: * Quick return if possible
157: *
158: IF( N.EQ.0 .OR. NRHS.EQ.0 )
159: $ RETURN
160: *
161: * Determine the number of right-hand sides to solve at a time.
162: *
163: IF( NRHS.EQ.1 ) THEN
164: NB = 1
165: ELSE
166: NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
167: END IF
168: *
169: IF( NB.GE.NRHS ) THEN
170: CALL DPTTS2( N, NRHS, D, E, B, LDB )
171: ELSE
172: DO 10 J = 1, NRHS, NB
173: JB = MIN( NRHS-J+1, NB )
174: CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
175: 10 CONTINUE
176: END IF
177: *
178: RETURN
179: *
180: * End of DPTTRS
181: *
182: END
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