LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
dpbtrs.f
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1 *> \brief \b DPBTRS
2 *
3 * =========== DOCUMENTATION ===========
4 *
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17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE DPBTRS( UPLO, N, KD, NRHS, AB, LDAB, B, LDB, INFO )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER UPLO
25 * INTEGER INFO, KD, LDAB, LDB, N, NRHS
26 * ..
27 * .. Array Arguments ..
28 * DOUBLE PRECISION AB( LDAB, * ), B( LDB, * )
29 * ..
30 *
31 *
32 *> \par Purpose:
33 * =============
34 *>
35 *> \verbatim
36 *>
37 *> DPBTRS solves a system of linear equations A*X = B with a symmetric
38 *> positive definite band matrix A using the Cholesky factorization
39 *> A = U**T*U or A = L*L**T computed by DPBTRF.
40 *> \endverbatim
41 *
42 * Arguments:
43 * ==========
44 *
45 *> \param[in] UPLO
46 *> \verbatim
47 *> UPLO is CHARACTER*1
48 *> = 'U': Upper triangular factor stored in AB;
49 *> = 'L': Lower triangular factor stored in AB.
50 *> \endverbatim
51 *>
52 *> \param[in] N
53 *> \verbatim
54 *> N is INTEGER
55 *> The order of the matrix A. N >= 0.
56 *> \endverbatim
57 *>
58 *> \param[in] KD
59 *> \verbatim
60 *> KD is INTEGER
61 *> The number of superdiagonals of the matrix A if UPLO = 'U',
62 *> or the number of subdiagonals if UPLO = 'L'. KD >= 0.
63 *> \endverbatim
64 *>
65 *> \param[in] NRHS
66 *> \verbatim
67 *> NRHS is INTEGER
68 *> The number of right hand sides, i.e., the number of columns
69 *> of the matrix B. NRHS >= 0.
70 *> \endverbatim
71 *>
72 *> \param[in] AB
73 *> \verbatim
74 *> AB is DOUBLE PRECISION array, dimension (LDAB,N)
75 *> The triangular factor U or L from the Cholesky factorization
76 *> A = U**T*U or A = L*L**T of the band matrix A, stored in the
77 *> first KD+1 rows of the array. The j-th column of U or L is
78 *> stored in the j-th column of the array AB as follows:
79 *> if UPLO ='U', AB(kd+1+i-j,j) = U(i,j) for max(1,j-kd)<=i<=j;
80 *> if UPLO ='L', AB(1+i-j,j) = L(i,j) for j<=i<=min(n,j+kd).
81 *> \endverbatim
82 *>
83 *> \param[in] LDAB
84 *> \verbatim
85 *> LDAB is INTEGER
86 *> The leading dimension of the array AB. LDAB >= KD+1.
87 *> \endverbatim
88 *>
89 *> \param[in,out] B
90 *> \verbatim
91 *> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
92 *> On entry, the right hand side matrix B.
93 *> On exit, the solution matrix X.
94 *> \endverbatim
95 *>
96 *> \param[in] LDB
97 *> \verbatim
98 *> LDB is INTEGER
99 *> The leading dimension of the array B. LDB >= max(1,N).
100 *> \endverbatim
101 *>
102 *> \param[out] INFO
103 *> \verbatim
104 *> INFO is INTEGER
105 *> = 0: successful exit
106 *> < 0: if INFO = -i, the i-th argument had an illegal value
107 *> \endverbatim
108 *
109 * Authors:
110 * ========
111 *
112 *> \author Univ. of Tennessee
113 *> \author Univ. of California Berkeley
114 *> \author Univ. of Colorado Denver
115 *> \author NAG Ltd.
116 *
117 *> \date November 2011
118 *
119 *> \ingroup doubleOTHERcomputational
120 *
121 * =====================================================================
122  SUBROUTINE dpbtrs( UPLO, N, KD, NRHS, AB, LDAB, B, LDB, INFO )
123 *
124 * -- LAPACK computational routine (version 3.4.0) --
125 * -- LAPACK is a software package provided by Univ. of Tennessee, --
126 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
127 * November 2011
128 *
129 * .. Scalar Arguments ..
130  CHARACTER UPLO
131  INTEGER INFO, KD, LDAB, LDB, N, NRHS
132 * ..
133 * .. Array Arguments ..
134  DOUBLE PRECISION AB( ldab, * ), B( ldb, * )
135 * ..
136 *
137 * =====================================================================
138 *
139 * .. Local Scalars ..
140  LOGICAL UPPER
141  INTEGER J
142 * ..
143 * .. External Functions ..
144  LOGICAL LSAME
145  EXTERNAL lsame
146 * ..
147 * .. External Subroutines ..
148  EXTERNAL dtbsv, xerbla
149 * ..
150 * .. Intrinsic Functions ..
151  INTRINSIC max
152 * ..
153 * .. Executable Statements ..
154 *
155 * Test the input parameters.
156 *
157  info = 0
158  upper = lsame( uplo, 'U' )
159  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
160  info = -1
161  ELSE IF( n.LT.0 ) THEN
162  info = -2
163  ELSE IF( kd.LT.0 ) THEN
164  info = -3
165  ELSE IF( nrhs.LT.0 ) THEN
166  info = -4
167  ELSE IF( ldab.LT.kd+1 ) THEN
168  info = -6
169  ELSE IF( ldb.LT.max( 1, n ) ) THEN
170  info = -8
171  END IF
172  IF( info.NE.0 ) THEN
173  CALL xerbla( 'DPBTRS', -info )
174  RETURN
175  END IF
176 *
177 * Quick return if possible
178 *
179  IF( n.EQ.0 .OR. nrhs.EQ.0 )
180  \$ RETURN
181 *
182  IF( upper ) THEN
183 *
184 * Solve A*X = B where A = U**T *U.
185 *
186  DO 10 j = 1, nrhs
187 *
188 * Solve U**T *X = B, overwriting B with X.
189 *
190  CALL dtbsv( 'Upper', 'Transpose', 'Non-unit', n, kd, ab,
191  \$ ldab, b( 1, j ), 1 )
192 *
193 * Solve U*X = B, overwriting B with X.
194 *
195  CALL dtbsv( 'Upper', 'No transpose', 'Non-unit', n, kd, ab,
196  \$ ldab, b( 1, j ), 1 )
197  10 CONTINUE
198  ELSE
199 *
200 * Solve A*X = B where A = L*L**T.
201 *
202  DO 20 j = 1, nrhs
203 *
204 * Solve L*X = B, overwriting B with X.
205 *
206  CALL dtbsv( 'Lower', 'No transpose', 'Non-unit', n, kd, ab,
207  \$ ldab, b( 1, j ), 1 )
208 *
209 * Solve L**T *X = B, overwriting B with X.
210 *
211  CALL dtbsv( 'Lower', 'Transpose', 'Non-unit', n, kd, ab,
212  \$ ldab, b( 1, j ), 1 )
213  20 CONTINUE
214  END IF
215 *
216  RETURN
217 *
218 * End of DPBTRS
219 *
220  END
subroutine dtbsv(UPLO, TRANS, DIAG, N, K, A, LDA, X, INCX)
DTBSV
Definition: dtbsv.f:191
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine dpbtrs(UPLO, N, KD, NRHS, AB, LDAB, B, LDB, INFO)
DPBTRS
Definition: dpbtrs.f:123