Annotation of rpl/lapack/lapack/dpttrs.f, revision 1.19
1.9 bertrand 1: *> \brief \b DPTTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
1.16 bertrand 5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
1.9 bertrand 7: *
8: *> \htmlonly
1.16 bertrand 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">
1.9 bertrand 15: *> [TXT]</a>
1.16 bertrand 16: *> \endhtmlonly
1.9 bertrand 17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
1.16 bertrand 22: *
1.9 bertrand 23: * .. Scalar Arguments ..
24: * INTEGER INFO, LDB, N, NRHS
25: * ..
26: * .. Array Arguments ..
27: * DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
28: * ..
1.16 bertrand 29: *
1.9 bertrand 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: *
1.16 bertrand 100: *> \author Univ. of Tennessee
101: *> \author Univ. of California Berkeley
102: *> \author Univ. of Colorado Denver
103: *> \author NAG Ltd.
1.9 bertrand 104: *
1.12 bertrand 105: *> \ingroup doublePTcomputational
1.9 bertrand 106: *
107: * =====================================================================
1.1 bertrand 108: SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
109: *
1.19 ! bertrand 110: * -- LAPACK computational routine --
1.1 bertrand 111: * -- LAPACK is a software package provided by Univ. of Tennessee, --
112: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
113: *
114: * .. Scalar Arguments ..
115: INTEGER INFO, LDB, N, NRHS
116: * ..
117: * .. Array Arguments ..
118: DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
119: * ..
120: *
121: * =====================================================================
122: *
123: * .. Local Scalars ..
124: INTEGER J, JB, NB
125: * ..
126: * .. External Functions ..
127: INTEGER ILAENV
128: EXTERNAL ILAENV
129: * ..
130: * .. External Subroutines ..
131: EXTERNAL DPTTS2, XERBLA
132: * ..
133: * .. Intrinsic Functions ..
134: INTRINSIC MAX, MIN
135: * ..
136: * .. Executable Statements ..
137: *
138: * Test the input arguments.
139: *
140: INFO = 0
141: IF( N.LT.0 ) THEN
142: INFO = -1
143: ELSE IF( NRHS.LT.0 ) THEN
144: INFO = -2
145: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
146: INFO = -6
147: END IF
148: IF( INFO.NE.0 ) THEN
149: CALL XERBLA( 'DPTTRS', -INFO )
150: RETURN
151: END IF
152: *
153: * Quick return if possible
154: *
155: IF( N.EQ.0 .OR. NRHS.EQ.0 )
156: $ RETURN
157: *
158: * Determine the number of right-hand sides to solve at a time.
159: *
160: IF( NRHS.EQ.1 ) THEN
161: NB = 1
162: ELSE
163: NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
164: END IF
165: *
166: IF( NB.GE.NRHS ) THEN
167: CALL DPTTS2( N, NRHS, D, E, B, LDB )
168: ELSE
169: DO 10 J = 1, NRHS, NB
170: JB = MIN( NRHS-J+1, NB )
171: CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
172: 10 CONTINUE
173: END IF
174: *
175: RETURN
176: *
177: * End of DPTTRS
178: *
179: END
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