Annotation of rpl/lapack/lapack/dtptrs.f, revision 1.18
1.9 bertrand 1: *> \brief \b DTPTRS
2: *
3: * =========== DOCUMENTATION ===========
4: *
1.15 bertrand 5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
1.9 bertrand 7: *
8: *> \htmlonly
1.15 bertrand 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">
1.9 bertrand 15: *> [TXT]</a>
1.15 bertrand 16: *> \endhtmlonly
1.9 bertrand 17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
1.15 bertrand 22: *
1.9 bertrand 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: * ..
1.15 bertrand 30: *
1.9 bertrand 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: *
1.15 bertrand 121: *> \author Univ. of Tennessee
122: *> \author Univ. of California Berkeley
123: *> \author Univ. of Colorado Denver
124: *> \author NAG Ltd.
1.9 bertrand 125: *
126: *> \ingroup doubleOTHERcomputational
127: *
128: * =====================================================================
1.1 bertrand 129: SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
130: *
1.18 ! bertrand 131: * -- LAPACK computational routine --
1.1 bertrand 132: * -- LAPACK is a software package provided by Univ. of Tennessee, --
133: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
134: *
135: * .. Scalar Arguments ..
136: CHARACTER DIAG, TRANS, UPLO
137: INTEGER INFO, LDB, N, NRHS
138: * ..
139: * .. Array Arguments ..
140: DOUBLE PRECISION AP( * ), B( LDB, * )
141: * ..
142: *
143: * =====================================================================
144: *
145: * .. Parameters ..
146: DOUBLE PRECISION ZERO
147: PARAMETER ( ZERO = 0.0D+0 )
148: * ..
149: * .. Local Scalars ..
150: LOGICAL NOUNIT, UPPER
151: INTEGER J, JC
152: * ..
153: * .. External Functions ..
154: LOGICAL LSAME
155: EXTERNAL LSAME
156: * ..
157: * .. External Subroutines ..
158: EXTERNAL DTPSV, XERBLA
159: * ..
160: * .. Intrinsic Functions ..
161: INTRINSIC MAX
162: * ..
163: * .. Executable Statements ..
164: *
165: * Test the input parameters.
166: *
167: INFO = 0
168: UPPER = LSAME( UPLO, 'U' )
169: NOUNIT = LSAME( DIAG, 'N' )
170: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
171: INFO = -1
172: ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
173: $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
174: INFO = -2
175: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
176: INFO = -3
177: ELSE IF( N.LT.0 ) THEN
178: INFO = -4
179: ELSE IF( NRHS.LT.0 ) THEN
180: INFO = -5
181: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
182: INFO = -8
183: END IF
184: IF( INFO.NE.0 ) THEN
185: CALL XERBLA( 'DTPTRS', -INFO )
186: RETURN
187: END IF
188: *
189: * Quick return if possible
190: *
191: IF( N.EQ.0 )
192: $ RETURN
193: *
194: * Check for singularity.
195: *
196: IF( NOUNIT ) THEN
197: IF( UPPER ) THEN
198: JC = 1
199: DO 10 INFO = 1, N
200: IF( AP( JC+INFO-1 ).EQ.ZERO )
201: $ RETURN
202: JC = JC + INFO
203: 10 CONTINUE
204: ELSE
205: JC = 1
206: DO 20 INFO = 1, N
207: IF( AP( JC ).EQ.ZERO )
208: $ RETURN
209: JC = JC + N - INFO + 1
210: 20 CONTINUE
211: END IF
212: END IF
213: INFO = 0
214: *
1.8 bertrand 215: * Solve A * x = b or A**T * x = b.
1.1 bertrand 216: *
217: DO 30 J = 1, NRHS
218: CALL DTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
219: 30 CONTINUE
220: *
221: RETURN
222: *
223: * End of DTPTRS
224: *
225: END
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