 |
LAPACK 3.3.1
Linear Algebra PACKage
|
|
LAPACK 3.3.1
Linear Algebra PACKage
|
00001 SUBROUTINE DLAPTM( N, NRHS, ALPHA, D, E, X, LDX, BETA, B, LDB ) 00002 * 00003 * -- LAPACK auxiliary routine (version 3.1) -- 00004 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. 00005 * November 2006 00006 * 00007 * .. Scalar Arguments .. 00008 INTEGER LDB, LDX, N, NRHS 00009 DOUBLE PRECISION ALPHA, BETA 00010 * .. 00011 * .. Array Arguments .. 00012 DOUBLE PRECISION B( LDB, * ), D( * ), E( * ), X( LDX, * ) 00013 * .. 00014 * 00015 * Purpose 00016 * ======= 00017 * 00018 * DLAPTM multiplies an N by NRHS matrix X by a symmetric tridiagonal 00019 * matrix A and stores the result in a matrix B. The operation has the 00020 * form 00021 * 00022 * B := alpha * A * X + beta * B 00023 * 00024 * where alpha may be either 1. or -1. and beta may be 0., 1., or -1. 00025 * 00026 * Arguments 00027 * ========= 00028 * 00029 * N (input) INTEGER 00030 * The order of the matrix A. N >= 0. 00031 * 00032 * NRHS (input) INTEGER 00033 * The number of right hand sides, i.e., the number of columns 00034 * of the matrices X and B. 00035 * 00036 * ALPHA (input) DOUBLE PRECISION 00037 * The scalar alpha. ALPHA must be 1. or -1.; otherwise, 00038 * it is assumed to be 0. 00039 * 00040 * D (input) DOUBLE PRECISION array, dimension (N) 00041 * The n diagonal elements of the tridiagonal matrix A. 00042 * 00043 * E (input) DOUBLE PRECISION array, dimension (N-1) 00044 * The (n-1) subdiagonal or superdiagonal elements of A. 00045 * 00046 * X (input) DOUBLE PRECISION array, dimension (LDX,NRHS) 00047 * The N by NRHS matrix X. 00048 * 00049 * LDX (input) INTEGER 00050 * The leading dimension of the array X. LDX >= max(N,1). 00051 * 00052 * BETA (input) DOUBLE PRECISION 00053 * The scalar beta. BETA must be 0., 1., or -1.; otherwise, 00054 * it is assumed to be 1. 00055 * 00056 * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) 00057 * On entry, the N by NRHS matrix B. 00058 * On exit, B is overwritten by the matrix expression 00059 * B := alpha * A * X + beta * B. 00060 * 00061 * LDB (input) INTEGER 00062 * The leading dimension of the array B. LDB >= max(N,1). 00063 * 00064 * ===================================================================== 00065 * 00066 * .. Parameters .. 00067 DOUBLE PRECISION ONE, ZERO 00068 PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) 00069 * .. 00070 * .. Local Scalars .. 00071 INTEGER I, J 00072 * .. 00073 * .. Executable Statements .. 00074 * 00075 IF( N.EQ.0 ) 00076 $ RETURN 00077 * 00078 * Multiply B by BETA if BETA.NE.1. 00079 * 00080 IF( BETA.EQ.ZERO ) THEN 00081 DO 20 J = 1, NRHS 00082 DO 10 I = 1, N 00083 B( I, J ) = ZERO 00084 10 CONTINUE 00085 20 CONTINUE 00086 ELSE IF( BETA.EQ.-ONE ) THEN 00087 DO 40 J = 1, NRHS 00088 DO 30 I = 1, N 00089 B( I, J ) = -B( I, J ) 00090 30 CONTINUE 00091 40 CONTINUE 00092 END IF 00093 * 00094 IF( ALPHA.EQ.ONE ) THEN 00095 * 00096 * Compute B := B + A*X 00097 * 00098 DO 60 J = 1, NRHS 00099 IF( N.EQ.1 ) THEN 00100 B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) 00101 ELSE 00102 B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) + 00103 $ E( 1 )*X( 2, J ) 00104 B( N, J ) = B( N, J ) + E( N-1 )*X( N-1, J ) + 00105 $ D( N )*X( N, J ) 00106 DO 50 I = 2, N - 1 00107 B( I, J ) = B( I, J ) + E( I-1 )*X( I-1, J ) + 00108 $ D( I )*X( I, J ) + E( I )*X( I+1, J ) 00109 50 CONTINUE 00110 END IF 00111 60 CONTINUE 00112 ELSE IF( ALPHA.EQ.-ONE ) THEN 00113 * 00114 * Compute B := B - A*X 00115 * 00116 DO 80 J = 1, NRHS 00117 IF( N.EQ.1 ) THEN 00118 B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) 00119 ELSE 00120 B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) - 00121 $ E( 1 )*X( 2, J ) 00122 B( N, J ) = B( N, J ) - E( N-1 )*X( N-1, J ) - 00123 $ D( N )*X( N, J ) 00124 DO 70 I = 2, N - 1 00125 B( I, J ) = B( I, J ) - E( I-1 )*X( I-1, J ) - 00126 $ D( I )*X( I, J ) - E( I )*X( I+1, J ) 00127 70 CONTINUE 00128 END IF 00129 80 CONTINUE 00130 END IF 00131 RETURN 00132 * 00133 * End of DLAPTM 00134 * 00135 END
1.7.3 
