LAPACK 3.12.0 LAPACK: Linear Algebra PACKage
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sptsv.f
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1*> \brief <b> SPTSV computes the solution to system of linear equations A * X = B for PT matrices</b>
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/sptsv.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/sptsv.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/sptsv.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE SPTSV( N, NRHS, D, E, B, LDB, INFO )
22*
23* .. Scalar Arguments ..
24* INTEGER INFO, LDB, N, NRHS
25* ..
26* .. Array Arguments ..
27* REAL B( LDB, * ), D( * ), E( * )
28* ..
29*
30*
31*> \par Purpose:
32* =============
33*>
34*> \verbatim
35*>
36*> SPTSV computes the solution to a real system of linear equations
37*> A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
38*> matrix, and X and B are N-by-NRHS matrices.
39*>
40*> A is factored as A = L*D*L**T, and the factored form of A is then
41*> used to solve the system of equations.
42*> \endverbatim
43*
44* Arguments:
45* ==========
46*
47*> \param[in] N
48*> \verbatim
49*> N is INTEGER
50*> The order of the 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,out] D
61*> \verbatim
62*> D is REAL array, dimension (N)
63*> On entry, the n diagonal elements of the tridiagonal matrix
64*> A. On exit, the n diagonal elements of the diagonal matrix
65*> D from the factorization A = L*D*L**T.
66*> \endverbatim
67*>
68*> \param[in,out] E
69*> \verbatim
70*> E is REAL array, dimension (N-1)
71*> On entry, the (n-1) subdiagonal elements of the tridiagonal
72*> matrix A. On exit, the (n-1) subdiagonal elements of the
73*> unit bidiagonal factor L from the L*D*L**T factorization of
74*> A. (E can also be regarded as the superdiagonal of the unit
75*> bidiagonal factor U from the U**T*D*U factorization of A.)
76*> \endverbatim
77*>
78*> \param[in,out] B
79*> \verbatim
80*> B is REAL array, dimension (LDB,NRHS)
81*> On entry, the N-by-NRHS right hand side matrix B.
82*> On exit, if INFO = 0, the N-by-NRHS solution matrix X.
83*> \endverbatim
84*>
85*> \param[in] LDB
86*> \verbatim
87*> LDB is INTEGER
88*> The leading dimension of the array B. LDB >= max(1,N).
89*> \endverbatim
90*>
91*> \param[out] INFO
92*> \verbatim
93*> INFO is INTEGER
94*> = 0: successful exit
95*> < 0: if INFO = -i, the i-th argument had an illegal value
96*> > 0: if INFO = i, the leading principal minor of order i
97*> is not positive, and the solution has not been
98*> computed. The factorization has not been completed
99*> unless i = N.
100*> \endverbatim
101*
102* Authors:
103* ========
104*
105*> \author Univ. of Tennessee
106*> \author Univ. of California Berkeley
107*> \author Univ. of Colorado Denver
108*> \author NAG Ltd.
109*
110*> \ingroup ptsv
111*
112* =====================================================================
113 SUBROUTINE sptsv( N, NRHS, D, E, B, LDB, INFO )
114*
115* -- LAPACK driver routine --
116* -- LAPACK is a software package provided by Univ. of Tennessee, --
117* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
118*
119* .. Scalar Arguments ..
120 INTEGER INFO, LDB, N, NRHS
121* ..
122* .. Array Arguments ..
123 REAL B( LDB, * ), D( * ), E( * )
124* ..
125*
126* =====================================================================
127*
128* .. External Subroutines ..
129 EXTERNAL spttrf, spttrs, xerbla
130* ..
131* .. Intrinsic Functions ..
132 INTRINSIC max
133* ..
134* .. Executable Statements ..
135*
136* Test the input parameters.
137*
138 info = 0
139 IF( n.LT.0 ) THEN
140 info = -1
141 ELSE IF( nrhs.LT.0 ) THEN
142 info = -2
143 ELSE IF( ldb.LT.max( 1, n ) ) THEN
144 info = -6
145 END IF
146 IF( info.NE.0 ) THEN
147 CALL xerbla( 'SPTSV ', -info )
148 RETURN
149 END IF
150*
151* Compute the L*D*L**T (or U**T*D*U) factorization of A.
152*
153 CALL spttrf( n, d, e, info )
154 IF( info.EQ.0 ) THEN
155*
156* Solve the system A*X = B, overwriting B with X.
157*
158 CALL spttrs( n, nrhs, d, e, b, ldb, info )
159 END IF
160 RETURN
161*
162* End of SPTSV
163*
164 END
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine sptsv(n, nrhs, d, e, b, ldb, info)
SPTSV computes the solution to system of linear equations A * X = B for PT matrices
Definition sptsv.f:114
subroutine spttrf(n, d, e, info)
SPTTRF
Definition spttrf.f:91
subroutine spttrs(n, nrhs, d, e, b, ldb, info)
SPTTRS
Definition spttrs.f:109