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LAPACK 3.3.1
Linear Algebra PACKage
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LAPACK 3.3.1
Linear Algebra PACKage
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00001 SUBROUTINE CGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB, 00002 $ INFO ) 00003 * 00004 * -- LAPACK routine (version 3.2) -- 00005 * -- LAPACK is a software package provided by Univ. of Tennessee, -- 00006 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 00007 * November 2006 00008 * 00009 * .. Scalar Arguments .. 00010 CHARACTER TRANS 00011 INTEGER INFO, LDB, N, NRHS 00012 * .. 00013 * .. Array Arguments .. 00014 INTEGER IPIV( * ) 00015 COMPLEX B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * ) 00016 * .. 00017 * 00018 * Purpose 00019 * ======= 00020 * 00021 * CGTTRS solves one of the systems of equations 00022 * A * X = B, A**T * X = B, or A**H * X = B, 00023 * with a tridiagonal matrix A using the LU factorization computed 00024 * by CGTTRF. 00025 * 00026 * Arguments 00027 * ========= 00028 * 00029 * TRANS (input) CHARACTER*1 00030 * Specifies the form of the system of equations. 00031 * = 'N': A * X = B (No transpose) 00032 * = 'T': A**T * X = B (Transpose) 00033 * = 'C': A**H * X = B (Conjugate transpose) 00034 * 00035 * N (input) INTEGER 00036 * The order of the matrix A. 00037 * 00038 * NRHS (input) INTEGER 00039 * The number of right hand sides, i.e., the number of columns 00040 * of the matrix B. NRHS >= 0. 00041 * 00042 * DL (input) COMPLEX array, dimension (N-1) 00043 * The (n-1) multipliers that define the matrix L from the 00044 * LU factorization of A. 00045 * 00046 * D (input) COMPLEX array, dimension (N) 00047 * The n diagonal elements of the upper triangular matrix U from 00048 * the LU factorization of A. 00049 * 00050 * DU (input) COMPLEX array, dimension (N-1) 00051 * The (n-1) elements of the first super-diagonal of U. 00052 * 00053 * DU2 (input) COMPLEX array, dimension (N-2) 00054 * The (n-2) elements of the second super-diagonal of U. 00055 * 00056 * IPIV (input) INTEGER array, dimension (N) 00057 * The pivot indices; for 1 <= i <= n, row i of the matrix was 00058 * interchanged with row IPIV(i). IPIV(i) will always be either 00059 * i or i+1; IPIV(i) = i indicates a row interchange was not 00060 * required. 00061 * 00062 * B (input/output) COMPLEX array, dimension (LDB,NRHS) 00063 * On entry, the matrix of right hand side vectors B. 00064 * On exit, B is overwritten by the solution vectors X. 00065 * 00066 * LDB (input) INTEGER 00067 * The leading dimension of the array B. LDB >= max(1,N). 00068 * 00069 * INFO (output) INTEGER 00070 * = 0: successful exit 00071 * < 0: if INFO = -k, the k-th argument had an illegal value 00072 * 00073 * ===================================================================== 00074 * 00075 * .. Local Scalars .. 00076 LOGICAL NOTRAN 00077 INTEGER ITRANS, J, JB, NB 00078 * .. 00079 * .. External Functions .. 00080 INTEGER ILAENV 00081 EXTERNAL ILAENV 00082 * .. 00083 * .. External Subroutines .. 00084 EXTERNAL CGTTS2, XERBLA 00085 * .. 00086 * .. Intrinsic Functions .. 00087 INTRINSIC MAX, MIN 00088 * .. 00089 * .. Executable Statements .. 00090 * 00091 INFO = 0 00092 NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' ) 00093 IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ. 00094 $ 't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN 00095 INFO = -1 00096 ELSE IF( N.LT.0 ) THEN 00097 INFO = -2 00098 ELSE IF( NRHS.LT.0 ) THEN 00099 INFO = -3 00100 ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN 00101 INFO = -10 00102 END IF 00103 IF( INFO.NE.0 ) THEN 00104 CALL XERBLA( 'CGTTRS', -INFO ) 00105 RETURN 00106 END IF 00107 * 00108 * Quick return if possible 00109 * 00110 IF( N.EQ.0 .OR. NRHS.EQ.0 ) 00111 $ RETURN 00112 * 00113 * Decode TRANS 00114 * 00115 IF( NOTRAN ) THEN 00116 ITRANS = 0 00117 ELSE IF( TRANS.EQ.'T' .OR. TRANS.EQ.'t' ) THEN 00118 ITRANS = 1 00119 ELSE 00120 ITRANS = 2 00121 END IF 00122 * 00123 * Determine the number of right-hand sides to solve at a time. 00124 * 00125 IF( NRHS.EQ.1 ) THEN 00126 NB = 1 00127 ELSE 00128 NB = MAX( 1, ILAENV( 1, 'CGTTRS', TRANS, N, NRHS, -1, -1 ) ) 00129 END IF 00130 * 00131 IF( NB.GE.NRHS ) THEN 00132 CALL CGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB ) 00133 ELSE 00134 DO 10 J = 1, NRHS, NB 00135 JB = MIN( NRHS-J+1, NB ) 00136 CALL CGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ), 00137 $ LDB ) 00138 10 CONTINUE 00139 END IF 00140 * 00141 * End of CGTTRS 00142 * 00143 END
1.7.3 
