Annotation of rpl/lapack/lapack/dtptrs.f, revision 1.14
1.9 bertrand 1: *> \brief \b DTPTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download DTPTRS + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dtptrs.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dtptrs.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dtptrs.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
22: *
23: * .. Scalar Arguments ..
24: * CHARACTER DIAG, TRANS, UPLO
25: * INTEGER INFO, LDB, N, NRHS
26: * ..
27: * .. Array Arguments ..
28: * DOUBLE PRECISION AP( * ), B( LDB, * )
29: * ..
30: *
31: *
32: *> \par Purpose:
33: * =============
34: *>
35: *> \verbatim
36: *>
37: *> DTPTRS solves a triangular system of the form
38: *>
39: *> A * X = B or A**T * X = B,
40: *>
41: *> where A is a triangular matrix of order N stored in packed format,
42: *> and B is an N-by-NRHS matrix. A check is made to verify that A is
43: *> nonsingular.
44: *> \endverbatim
45: *
46: * Arguments:
47: * ==========
48: *
49: *> \param[in] UPLO
50: *> \verbatim
51: *> UPLO is CHARACTER*1
52: *> = 'U': A is upper triangular;
53: *> = 'L': A is lower triangular.
54: *> \endverbatim
55: *>
56: *> \param[in] TRANS
57: *> \verbatim
58: *> TRANS is CHARACTER*1
59: *> Specifies the form of the system of equations:
60: *> = 'N': A * X = B (No transpose)
61: *> = 'T': A**T * X = B (Transpose)
62: *> = 'C': A**H * X = B (Conjugate transpose = Transpose)
63: *> \endverbatim
64: *>
65: *> \param[in] DIAG
66: *> \verbatim
67: *> DIAG is CHARACTER*1
68: *> = 'N': A is non-unit triangular;
69: *> = 'U': A is unit triangular.
70: *> \endverbatim
71: *>
72: *> \param[in] N
73: *> \verbatim
74: *> N is INTEGER
75: *> The order of the matrix A. N >= 0.
76: *> \endverbatim
77: *>
78: *> \param[in] NRHS
79: *> \verbatim
80: *> NRHS is INTEGER
81: *> The number of right hand sides, i.e., the number of columns
82: *> of the matrix B. NRHS >= 0.
83: *> \endverbatim
84: *>
85: *> \param[in] AP
86: *> \verbatim
87: *> AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
88: *> The upper or lower triangular matrix A, packed columnwise in
89: *> a linear array. The j-th column of A is stored in the array
90: *> AP as follows:
91: *> if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
92: *> if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
93: *> \endverbatim
94: *>
95: *> \param[in,out] B
96: *> \verbatim
97: *> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
98: *> On entry, the right hand side matrix B.
99: *> On exit, if INFO = 0, the solution matrix X.
100: *> \endverbatim
101: *>
102: *> \param[in] LDB
103: *> \verbatim
104: *> LDB is INTEGER
105: *> The leading dimension of the array B. LDB >= max(1,N).
106: *> \endverbatim
107: *>
108: *> \param[out] INFO
109: *> \verbatim
110: *> INFO is INTEGER
111: *> = 0: successful exit
112: *> < 0: if INFO = -i, the i-th argument had an illegal value
113: *> > 0: if INFO = i, the i-th diagonal element of A is zero,
114: *> indicating that the matrix is singular and the
115: *> solutions X have not been computed.
116: *> \endverbatim
117: *
118: * Authors:
119: * ========
120: *
121: *> \author Univ. of Tennessee
122: *> \author Univ. of California Berkeley
123: *> \author Univ. of Colorado Denver
124: *> \author NAG Ltd.
125: *
126: *> \date November 2011
127: *
128: *> \ingroup doubleOTHERcomputational
129: *
130: * =====================================================================
1.1 bertrand 131: SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
132: *
1.9 bertrand 133: * -- LAPACK computational routine (version 3.4.0) --
1.1 bertrand 134: * -- LAPACK is a software package provided by Univ. of Tennessee, --
135: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.9 bertrand 136: * November 2011
1.1 bertrand 137: *
138: * .. Scalar Arguments ..
139: CHARACTER DIAG, TRANS, UPLO
140: INTEGER INFO, LDB, N, NRHS
141: * ..
142: * .. Array Arguments ..
143: DOUBLE PRECISION AP( * ), B( LDB, * )
144: * ..
145: *
146: * =====================================================================
147: *
148: * .. Parameters ..
149: DOUBLE PRECISION ZERO
150: PARAMETER ( ZERO = 0.0D+0 )
151: * ..
152: * .. Local Scalars ..
153: LOGICAL NOUNIT, UPPER
154: INTEGER J, JC
155: * ..
156: * .. External Functions ..
157: LOGICAL LSAME
158: EXTERNAL LSAME
159: * ..
160: * .. External Subroutines ..
161: EXTERNAL DTPSV, XERBLA
162: * ..
163: * .. Intrinsic Functions ..
164: INTRINSIC MAX
165: * ..
166: * .. Executable Statements ..
167: *
168: * Test the input parameters.
169: *
170: INFO = 0
171: UPPER = LSAME( UPLO, 'U' )
172: NOUNIT = LSAME( DIAG, 'N' )
173: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
174: INFO = -1
175: ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
176: $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
177: INFO = -2
178: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
179: INFO = -3
180: ELSE IF( N.LT.0 ) THEN
181: INFO = -4
182: ELSE IF( NRHS.LT.0 ) THEN
183: INFO = -5
184: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
185: INFO = -8
186: END IF
187: IF( INFO.NE.0 ) THEN
188: CALL XERBLA( 'DTPTRS', -INFO )
189: RETURN
190: END IF
191: *
192: * Quick return if possible
193: *
194: IF( N.EQ.0 )
195: $ RETURN
196: *
197: * Check for singularity.
198: *
199: IF( NOUNIT ) THEN
200: IF( UPPER ) THEN
201: JC = 1
202: DO 10 INFO = 1, N
203: IF( AP( JC+INFO-1 ).EQ.ZERO )
204: $ RETURN
205: JC = JC + INFO
206: 10 CONTINUE
207: ELSE
208: JC = 1
209: DO 20 INFO = 1, N
210: IF( AP( JC ).EQ.ZERO )
211: $ RETURN
212: JC = JC + N - INFO + 1
213: 20 CONTINUE
214: END IF
215: END IF
216: INFO = 0
217: *
1.8 bertrand 218: * Solve A * x = b or A**T * x = b.
1.1 bertrand 219: *
220: DO 30 J = 1, NRHS
221: CALL DTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
222: 30 CONTINUE
223: *
224: RETURN
225: *
226: * End of DTPTRS
227: *
228: END
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