Annotation of rpl/lapack/lapack/dpttrs.f, revision 1.9
1.9 ! bertrand 1: *> \brief \b DPTTRS
! 2: *
! 3: * =========== DOCUMENTATION ===========
! 4: *
! 5: * Online html documentation available at
! 6: * http://www.netlib.org/lapack/explore-html/
! 7: *
! 8: *> \htmlonly
! 9: *> Download DPTTRS + dependencies
! 10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dpttrs.f">
! 11: *> [TGZ]</a>
! 12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dpttrs.f">
! 13: *> [ZIP]</a>
! 14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dpttrs.f">
! 15: *> [TXT]</a>
! 16: *> \endhtmlonly
! 17: *
! 18: * Definition:
! 19: * ===========
! 20: *
! 21: * SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
! 22: *
! 23: * .. Scalar Arguments ..
! 24: * INTEGER INFO, LDB, N, NRHS
! 25: * ..
! 26: * .. Array Arguments ..
! 27: * DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
! 28: * ..
! 29: *
! 30: *
! 31: *> \par Purpose:
! 32: * =============
! 33: *>
! 34: *> \verbatim
! 35: *>
! 36: *> DPTTRS solves a tridiagonal system of the form
! 37: *> A * X = B
! 38: *> using the L*D*L**T factorization of A computed by DPTTRF. D is a
! 39: *> diagonal matrix specified in the vector D, L is a unit bidiagonal
! 40: *> matrix whose subdiagonal is specified in the vector E, and X and B
! 41: *> are N by NRHS matrices.
! 42: *> \endverbatim
! 43: *
! 44: * Arguments:
! 45: * ==========
! 46: *
! 47: *> \param[in] N
! 48: *> \verbatim
! 49: *> N is INTEGER
! 50: *> The order of the tridiagonal 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] D
! 61: *> \verbatim
! 62: *> D is DOUBLE PRECISION array, dimension (N)
! 63: *> The n diagonal elements of the diagonal matrix D from the
! 64: *> L*D*L**T factorization of A.
! 65: *> \endverbatim
! 66: *>
! 67: *> \param[in] E
! 68: *> \verbatim
! 69: *> E is DOUBLE PRECISION array, dimension (N-1)
! 70: *> The (n-1) subdiagonal elements of the unit bidiagonal factor
! 71: *> L from the L*D*L**T factorization of A. E can also be regarded
! 72: *> as the superdiagonal of the unit bidiagonal factor U from the
! 73: *> factorization A = U**T*D*U.
! 74: *> \endverbatim
! 75: *>
! 76: *> \param[in,out] B
! 77: *> \verbatim
! 78: *> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
! 79: *> On entry, the right hand side vectors B for the system of
! 80: *> linear equations.
! 81: *> On exit, the solution vectors, X.
! 82: *> \endverbatim
! 83: *>
! 84: *> \param[in] LDB
! 85: *> \verbatim
! 86: *> LDB is INTEGER
! 87: *> The leading dimension of the array B. LDB >= max(1,N).
! 88: *> \endverbatim
! 89: *>
! 90: *> \param[out] INFO
! 91: *> \verbatim
! 92: *> INFO is INTEGER
! 93: *> = 0: successful exit
! 94: *> < 0: if INFO = -k, the k-th argument had an illegal value
! 95: *> \endverbatim
! 96: *
! 97: * Authors:
! 98: * ========
! 99: *
! 100: *> \author Univ. of Tennessee
! 101: *> \author Univ. of California Berkeley
! 102: *> \author Univ. of Colorado Denver
! 103: *> \author NAG Ltd.
! 104: *
! 105: *> \date November 2011
! 106: *
! 107: *> \ingroup doubleOTHERcomputational
! 108: *
! 109: * =====================================================================
1.1 bertrand 110: SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
111: *
1.9 ! bertrand 112: * -- LAPACK computational routine (version 3.4.0) --
1.1 bertrand 113: * -- LAPACK is a software package provided by Univ. of Tennessee, --
114: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.9 ! bertrand 115: * November 2011
1.1 bertrand 116: *
117: * .. Scalar Arguments ..
118: INTEGER INFO, LDB, N, NRHS
119: * ..
120: * .. Array Arguments ..
121: DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
122: * ..
123: *
124: * =====================================================================
125: *
126: * .. Local Scalars ..
127: INTEGER J, JB, NB
128: * ..
129: * .. External Functions ..
130: INTEGER ILAENV
131: EXTERNAL ILAENV
132: * ..
133: * .. External Subroutines ..
134: EXTERNAL DPTTS2, XERBLA
135: * ..
136: * .. Intrinsic Functions ..
137: INTRINSIC MAX, MIN
138: * ..
139: * .. Executable Statements ..
140: *
141: * Test the input arguments.
142: *
143: INFO = 0
144: IF( N.LT.0 ) THEN
145: INFO = -1
146: ELSE IF( NRHS.LT.0 ) THEN
147: INFO = -2
148: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
149: INFO = -6
150: END IF
151: IF( INFO.NE.0 ) THEN
152: CALL XERBLA( 'DPTTRS', -INFO )
153: RETURN
154: END IF
155: *
156: * Quick return if possible
157: *
158: IF( N.EQ.0 .OR. NRHS.EQ.0 )
159: $ RETURN
160: *
161: * Determine the number of right-hand sides to solve at a time.
162: *
163: IF( NRHS.EQ.1 ) THEN
164: NB = 1
165: ELSE
166: NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
167: END IF
168: *
169: IF( NB.GE.NRHS ) THEN
170: CALL DPTTS2( N, NRHS, D, E, B, LDB )
171: ELSE
172: DO 10 J = 1, NRHS, NB
173: JB = MIN( NRHS-J+1, NB )
174: CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
175: 10 CONTINUE
176: END IF
177: *
178: RETURN
179: *
180: * End of DPTTRS
181: *
182: END
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