1: *> \brief \b ZPTTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download ZPTTRS + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zpttrs.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zpttrs.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zpttrs.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE ZPTTRS( UPLO, N, NRHS, D, E, B, LDB, INFO )
22: *
23: * .. Scalar Arguments ..
24: * CHARACTER UPLO
25: * INTEGER INFO, LDB, N, NRHS
26: * ..
27: * .. Array Arguments ..
28: * DOUBLE PRECISION D( * )
29: * COMPLEX*16 B( LDB, * ), E( * )
30: * ..
31: *
32: *
33: *> \par Purpose:
34: * =============
35: *>
36: *> \verbatim
37: *>
38: *> ZPTTRS solves a tridiagonal system of the form
39: *> A * X = B
40: *> using the factorization A = U**H *D* U or A = L*D*L**H computed by ZPTTRF.
41: *> D is a diagonal matrix specified in the vector D, U (or L) is a unit
42: *> bidiagonal matrix whose superdiagonal (subdiagonal) is specified in
43: *> the vector E, and X and B are N by NRHS matrices.
44: *> \endverbatim
45: *
46: * Arguments:
47: * ==========
48: *
49: *> \param[in] UPLO
50: *> \verbatim
51: *> UPLO is CHARACTER*1
52: *> Specifies the form of the factorization and whether the
53: *> vector E is the superdiagonal of the upper bidiagonal factor
54: *> U or the subdiagonal of the lower bidiagonal factor L.
55: *> = 'U': A = U**H *D*U, E is the superdiagonal of U
56: *> = 'L': A = L*D*L**H, E is the subdiagonal of L
57: *> \endverbatim
58: *>
59: *> \param[in] N
60: *> \verbatim
61: *> N is INTEGER
62: *> The order of the tridiagonal matrix A. N >= 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] D
73: *> \verbatim
74: *> D is DOUBLE PRECISION array, dimension (N)
75: *> The n diagonal elements of the diagonal matrix D from the
76: *> factorization A = U**H *D*U or A = L*D*L**H.
77: *> \endverbatim
78: *>
79: *> \param[in] E
80: *> \verbatim
81: *> E is COMPLEX*16 array, dimension (N-1)
82: *> If UPLO = 'U', the (n-1) superdiagonal elements of the unit
83: *> bidiagonal factor U from the factorization A = U**H*D*U.
84: *> If UPLO = 'L', the (n-1) subdiagonal elements of the unit
85: *> bidiagonal factor L from the factorization A = L*D*L**H.
86: *> \endverbatim
87: *>
88: *> \param[in,out] B
89: *> \verbatim
90: *> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
91: *> On entry, the right hand side vectors B for the system of
92: *> linear equations.
93: *> On exit, the solution vectors, 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 = -k, the k-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 complex16OTHERcomputational
120: *
121: * =====================================================================
122: SUBROUTINE ZPTTRS( UPLO, N, NRHS, D, E, 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, LDB, N, NRHS
132: * ..
133: * .. Array Arguments ..
134: DOUBLE PRECISION D( * )
135: COMPLEX*16 B( LDB, * ), E( * )
136: * ..
137: *
138: * =====================================================================
139: *
140: * .. Local Scalars ..
141: LOGICAL UPPER
142: INTEGER IUPLO, J, JB, NB
143: * ..
144: * .. External Functions ..
145: INTEGER ILAENV
146: EXTERNAL ILAENV
147: * ..
148: * .. External Subroutines ..
149: EXTERNAL XERBLA, ZPTTS2
150: * ..
151: * .. Intrinsic Functions ..
152: INTRINSIC MAX, MIN
153: * ..
154: * .. Executable Statements ..
155: *
156: * Test the input arguments.
157: *
158: INFO = 0
159: UPPER = ( UPLO.EQ.'U' .OR. UPLO.EQ.'u' )
160: IF( .NOT.UPPER .AND. .NOT.( UPLO.EQ.'L' .OR. UPLO.EQ.'l' ) ) THEN
161: INFO = -1
162: ELSE IF( N.LT.0 ) THEN
163: INFO = -2
164: ELSE IF( NRHS.LT.0 ) THEN
165: INFO = -3
166: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
167: INFO = -7
168: END IF
169: IF( INFO.NE.0 ) THEN
170: CALL XERBLA( 'ZPTTRS', -INFO )
171: RETURN
172: END IF
173: *
174: * Quick return if possible
175: *
176: IF( N.EQ.0 .OR. NRHS.EQ.0 )
177: $ RETURN
178: *
179: * Determine the number of right-hand sides to solve at a time.
180: *
181: IF( NRHS.EQ.1 ) THEN
182: NB = 1
183: ELSE
184: NB = MAX( 1, ILAENV( 1, 'ZPTTRS', UPLO, N, NRHS, -1, -1 ) )
185: END IF
186: *
187: * Decode UPLO
188: *
189: IF( UPPER ) THEN
190: IUPLO = 1
191: ELSE
192: IUPLO = 0
193: END IF
194: *
195: IF( NB.GE.NRHS ) THEN
196: CALL ZPTTS2( IUPLO, N, NRHS, D, E, B, LDB )
197: ELSE
198: DO 10 J = 1, NRHS, NB
199: JB = MIN( NRHS-J+1, NB )
200: CALL ZPTTS2( IUPLO, N, JB, D, E, B( 1, J ), LDB )
201: 10 CONTINUE
202: END IF
203: *
204: RETURN
205: *
206: * End of ZPTTRS
207: *
208: END
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