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LAPACK
3.4.1
LAPACK: Linear Algebra PACKage
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00001 *> \brief \b SGETRS 00002 * 00003 * =========== DOCUMENTATION =========== 00004 * 00005 * Online html documentation available at 00006 * http://www.netlib.org/lapack/explore-html/ 00007 * 00008 *> \htmlonly 00009 *> Download SGETRS + dependencies 00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/sgetrs.f"> 00011 *> [TGZ]</a> 00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/sgetrs.f"> 00013 *> [ZIP]</a> 00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/sgetrs.f"> 00015 *> [TXT]</a> 00016 *> \endhtmlonly 00017 * 00018 * Definition: 00019 * =========== 00020 * 00021 * SUBROUTINE SGETRS( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO ) 00022 * 00023 * .. Scalar Arguments .. 00024 * CHARACTER TRANS 00025 * INTEGER INFO, LDA, LDB, N, NRHS 00026 * .. 00027 * .. Array Arguments .. 00028 * INTEGER IPIV( * ) 00029 * REAL A( LDA, * ), B( LDB, * ) 00030 * .. 00031 * 00032 * 00033 *> \par Purpose: 00034 * ============= 00035 *> 00036 *> \verbatim 00037 *> 00038 *> SGETRS solves a system of linear equations 00039 *> A * X = B or A**T * X = B 00040 *> with a general N-by-N matrix A using the LU factorization computed 00041 *> by SGETRF. 00042 *> \endverbatim 00043 * 00044 * Arguments: 00045 * ========== 00046 * 00047 *> \param[in] TRANS 00048 *> \verbatim 00049 *> TRANS is CHARACTER*1 00050 *> Specifies the form of the system of equations: 00051 *> = 'N': A * X = B (No transpose) 00052 *> = 'T': A**T* X = B (Transpose) 00053 *> = 'C': A**T* X = B (Conjugate transpose = Transpose) 00054 *> \endverbatim 00055 *> 00056 *> \param[in] N 00057 *> \verbatim 00058 *> N is INTEGER 00059 *> The order of the matrix A. N >= 0. 00060 *> \endverbatim 00061 *> 00062 *> \param[in] NRHS 00063 *> \verbatim 00064 *> NRHS is INTEGER 00065 *> The number of right hand sides, i.e., the number of columns 00066 *> of the matrix B. NRHS >= 0. 00067 *> \endverbatim 00068 *> 00069 *> \param[in] A 00070 *> \verbatim 00071 *> A is REAL array, dimension (LDA,N) 00072 *> The factors L and U from the factorization A = P*L*U 00073 *> as computed by SGETRF. 00074 *> \endverbatim 00075 *> 00076 *> \param[in] LDA 00077 *> \verbatim 00078 *> LDA is INTEGER 00079 *> The leading dimension of the array A. LDA >= max(1,N). 00080 *> \endverbatim 00081 *> 00082 *> \param[in] IPIV 00083 *> \verbatim 00084 *> IPIV is INTEGER array, dimension (N) 00085 *> The pivot indices from SGETRF; for 1<=i<=N, row i of the 00086 *> matrix was interchanged with row IPIV(i). 00087 *> \endverbatim 00088 *> 00089 *> \param[in,out] B 00090 *> \verbatim 00091 *> B is REAL array, dimension (LDB,NRHS) 00092 *> On entry, the right hand side matrix B. 00093 *> On exit, the solution matrix X. 00094 *> \endverbatim 00095 *> 00096 *> \param[in] LDB 00097 *> \verbatim 00098 *> LDB is INTEGER 00099 *> The leading dimension of the array B. LDB >= max(1,N). 00100 *> \endverbatim 00101 *> 00102 *> \param[out] INFO 00103 *> \verbatim 00104 *> INFO is INTEGER 00105 *> = 0: successful exit 00106 *> < 0: if INFO = -i, the i-th argument had an illegal value 00107 *> \endverbatim 00108 * 00109 * Authors: 00110 * ======== 00111 * 00112 *> \author Univ. of Tennessee 00113 *> \author Univ. of California Berkeley 00114 *> \author Univ. of Colorado Denver 00115 *> \author NAG Ltd. 00116 * 00117 *> \date November 2011 00118 * 00119 *> \ingroup realGEcomputational 00120 * 00121 * ===================================================================== 00122 SUBROUTINE SGETRS( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO ) 00123 * 00124 * -- LAPACK computational routine (version 3.4.0) -- 00125 * -- LAPACK is a software package provided by Univ. of Tennessee, -- 00126 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 00127 * November 2011 00128 * 00129 * .. Scalar Arguments .. 00130 CHARACTER TRANS 00131 INTEGER INFO, LDA, LDB, N, NRHS 00132 * .. 00133 * .. Array Arguments .. 00134 INTEGER IPIV( * ) 00135 REAL A( LDA, * ), B( LDB, * ) 00136 * .. 00137 * 00138 * ===================================================================== 00139 * 00140 * .. Parameters .. 00141 REAL ONE 00142 PARAMETER ( ONE = 1.0E+0 ) 00143 * .. 00144 * .. Local Scalars .. 00145 LOGICAL NOTRAN 00146 * .. 00147 * .. External Functions .. 00148 LOGICAL LSAME 00149 EXTERNAL LSAME 00150 * .. 00151 * .. External Subroutines .. 00152 EXTERNAL SLASWP, STRSM, XERBLA 00153 * .. 00154 * .. Intrinsic Functions .. 00155 INTRINSIC MAX 00156 * .. 00157 * .. Executable Statements .. 00158 * 00159 * Test the input parameters. 00160 * 00161 INFO = 0 00162 NOTRAN = LSAME( TRANS, 'N' ) 00163 IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) .AND. .NOT. 00164 $ LSAME( TRANS, 'C' ) ) THEN 00165 INFO = -1 00166 ELSE IF( N.LT.0 ) THEN 00167 INFO = -2 00168 ELSE IF( NRHS.LT.0 ) THEN 00169 INFO = -3 00170 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN 00171 INFO = -5 00172 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN 00173 INFO = -8 00174 END IF 00175 IF( INFO.NE.0 ) THEN 00176 CALL XERBLA( 'SGETRS', -INFO ) 00177 RETURN 00178 END IF 00179 * 00180 * Quick return if possible 00181 * 00182 IF( N.EQ.0 .OR. NRHS.EQ.0 ) 00183 $ RETURN 00184 * 00185 IF( NOTRAN ) THEN 00186 * 00187 * Solve A * X = B. 00188 * 00189 * Apply row interchanges to the right hand sides. 00190 * 00191 CALL SLASWP( NRHS, B, LDB, 1, N, IPIV, 1 ) 00192 * 00193 * Solve L*X = B, overwriting B with X. 00194 * 00195 CALL STRSM( 'Left', 'Lower', 'No transpose', 'Unit', N, NRHS, 00196 $ ONE, A, LDA, B, LDB ) 00197 * 00198 * Solve U*X = B, overwriting B with X. 00199 * 00200 CALL STRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N, 00201 $ NRHS, ONE, A, LDA, B, LDB ) 00202 ELSE 00203 * 00204 * Solve A**T * X = B. 00205 * 00206 * Solve U**T *X = B, overwriting B with X. 00207 * 00208 CALL STRSM( 'Left', 'Upper', 'Transpose', 'Non-unit', N, NRHS, 00209 $ ONE, A, LDA, B, LDB ) 00210 * 00211 * Solve L**T *X = B, overwriting B with X. 00212 * 00213 CALL STRSM( 'Left', 'Lower', 'Transpose', 'Unit', N, NRHS, ONE, 00214 $ A, LDA, B, LDB ) 00215 * 00216 * Apply row interchanges to the solution vectors. 00217 * 00218 CALL SLASWP( NRHS, B, LDB, 1, N, IPIV, -1 ) 00219 END IF 00220 * 00221 RETURN 00222 * 00223 * End of SGETRS 00224 * 00225 END