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LAPACK
3.4.1
LAPACK: Linear Algebra PACKage
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00001 *> \brief \b SPTTRS 00002 * 00003 * =========== DOCUMENTATION =========== 00004 * 00005 * Online html documentation available at 00006 * http://www.netlib.org/lapack/explore-html/ 00007 * 00008 *> \htmlonly 00009 *> Download SPTTRS + dependencies 00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/spttrs.f"> 00011 *> [TGZ]</a> 00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/spttrs.f"> 00013 *> [ZIP]</a> 00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/spttrs.f"> 00015 *> [TXT]</a> 00016 *> \endhtmlonly 00017 * 00018 * Definition: 00019 * =========== 00020 * 00021 * SUBROUTINE SPTTRS( N, NRHS, D, E, B, LDB, INFO ) 00022 * 00023 * .. Scalar Arguments .. 00024 * INTEGER INFO, LDB, N, NRHS 00025 * .. 00026 * .. Array Arguments .. 00027 * REAL B( LDB, * ), D( * ), E( * ) 00028 * .. 00029 * 00030 * 00031 *> \par Purpose: 00032 * ============= 00033 *> 00034 *> \verbatim 00035 *> 00036 *> SPTTRS solves a tridiagonal system of the form 00037 *> A * X = B 00038 *> using the L*D*L**T factorization of A computed by SPTTRF. D is a 00039 *> diagonal matrix specified in the vector D, L is a unit bidiagonal 00040 *> matrix whose subdiagonal is specified in the vector E, and X and B 00041 *> are N by NRHS matrices. 00042 *> \endverbatim 00043 * 00044 * Arguments: 00045 * ========== 00046 * 00047 *> \param[in] N 00048 *> \verbatim 00049 *> N is INTEGER 00050 *> The order of the tridiagonal matrix A. N >= 0. 00051 *> \endverbatim 00052 *> 00053 *> \param[in] NRHS 00054 *> \verbatim 00055 *> NRHS is INTEGER 00056 *> The number of right hand sides, i.e., the number of columns 00057 *> of the matrix B. NRHS >= 0. 00058 *> \endverbatim 00059 *> 00060 *> \param[in] D 00061 *> \verbatim 00062 *> D is REAL array, dimension (N) 00063 *> The n diagonal elements of the diagonal matrix D from the 00064 *> L*D*L**T factorization of A. 00065 *> \endverbatim 00066 *> 00067 *> \param[in] E 00068 *> \verbatim 00069 *> E is REAL array, dimension (N-1) 00070 *> The (n-1) subdiagonal elements of the unit bidiagonal factor 00071 *> L from the L*D*L**T factorization of A. E can also be regarded 00072 *> as the superdiagonal of the unit bidiagonal factor U from the 00073 *> factorization A = U**T*D*U. 00074 *> \endverbatim 00075 *> 00076 *> \param[in,out] B 00077 *> \verbatim 00078 *> B is REAL array, dimension (LDB,NRHS) 00079 *> On entry, the right hand side vectors B for the system of 00080 *> linear equations. 00081 *> On exit, the solution vectors, X. 00082 *> \endverbatim 00083 *> 00084 *> \param[in] LDB 00085 *> \verbatim 00086 *> LDB is INTEGER 00087 *> The leading dimension of the array B. LDB >= max(1,N). 00088 *> \endverbatim 00089 *> 00090 *> \param[out] INFO 00091 *> \verbatim 00092 *> INFO is INTEGER 00093 *> = 0: successful exit 00094 *> < 0: if INFO = -k, the k-th argument had an illegal value 00095 *> \endverbatim 00096 * 00097 * Authors: 00098 * ======== 00099 * 00100 *> \author Univ. of Tennessee 00101 *> \author Univ. of California Berkeley 00102 *> \author Univ. of Colorado Denver 00103 *> \author NAG Ltd. 00104 * 00105 *> \date November 2011 00106 * 00107 *> \ingroup realOTHERcomputational 00108 * 00109 * ===================================================================== 00110 SUBROUTINE SPTTRS( N, NRHS, D, E, B, LDB, INFO ) 00111 * 00112 * -- LAPACK computational routine (version 3.4.0) -- 00113 * -- LAPACK is a software package provided by Univ. of Tennessee, -- 00114 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 00115 * November 2011 00116 * 00117 * .. Scalar Arguments .. 00118 INTEGER INFO, LDB, N, NRHS 00119 * .. 00120 * .. Array Arguments .. 00121 REAL B( LDB, * ), D( * ), E( * ) 00122 * .. 00123 * 00124 * ===================================================================== 00125 * 00126 * .. Local Scalars .. 00127 INTEGER J, JB, NB 00128 * .. 00129 * .. External Functions .. 00130 INTEGER ILAENV 00131 EXTERNAL ILAENV 00132 * .. 00133 * .. External Subroutines .. 00134 EXTERNAL SPTTS2, XERBLA 00135 * .. 00136 * .. Intrinsic Functions .. 00137 INTRINSIC MAX, MIN 00138 * .. 00139 * .. Executable Statements .. 00140 * 00141 * Test the input arguments. 00142 * 00143 INFO = 0 00144 IF( N.LT.0 ) THEN 00145 INFO = -1 00146 ELSE IF( NRHS.LT.0 ) THEN 00147 INFO = -2 00148 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN 00149 INFO = -6 00150 END IF 00151 IF( INFO.NE.0 ) THEN 00152 CALL XERBLA( 'SPTTRS', -INFO ) 00153 RETURN 00154 END IF 00155 * 00156 * Quick return if possible 00157 * 00158 IF( N.EQ.0 .OR. NRHS.EQ.0 ) 00159 $ RETURN 00160 * 00161 * Determine the number of right-hand sides to solve at a time. 00162 * 00163 IF( NRHS.EQ.1 ) THEN 00164 NB = 1 00165 ELSE 00166 NB = MAX( 1, ILAENV( 1, 'SPTTRS', ' ', N, NRHS, -1, -1 ) ) 00167 END IF 00168 * 00169 IF( NB.GE.NRHS ) THEN 00170 CALL SPTTS2( N, NRHS, D, E, B, LDB ) 00171 ELSE 00172 DO 10 J = 1, NRHS, NB 00173 JB = MIN( NRHS-J+1, NB ) 00174 CALL SPTTS2( N, JB, D, E, B( 1, J ), LDB ) 00175 10 CONTINUE 00176 END IF 00177 * 00178 RETURN 00179 * 00180 * End of SPTTRS 00181 * 00182 END