lapack-3.3.1/TESTING/LIN/slaptm.f

       1
       2
       3
       4
       5
       6
       7
       8
       9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      27
      28
      29
      30
      31
      32
      33
      34
      35
      36
      37
      38
      39
      40
      41
      42
      43
      44
      45
      46
      47
      48
      49
      50
      51
      52
      53
      54
      55
      56
      57
      58
      59
      60
      61
      62
      63
      64
      65
      66
      67
      68
      69
      70
      71
      72
      73
      74
      75
      76
      77
      78
      79
      80
      81
      82
      83
      84
      85
      86
      87
      88
      89
      90
      91
      92
      93
      94
      95
      96
      97
      98
      99
     100
     101
     102
     103
     104
     105
     106
     107
     108
     109
     110
     111
     112
     113
     114
     115
     116
     117
     118
     119
     120
     121
     122
     123
     124
     125
     126
     127
     128
     129
     130
     131
     132
     133
     134
     135

      SUBROUTINE SLAPTM( N, NRHS, ALPHA, D, E, X, LDX, BETA, B, LDB )
*
*  -- LAPACK auxiliary routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
      INTEGER            LDB, LDX, N, NRHS
      REAL               ALPHA, BETA
*     ..
*     .. Array Arguments ..
      REAL               B( LDB, * ), D( * ), E( * ), X( LDX, * )
*     ..
*
*  Purpose
*  =======
*
*  SLAPTM multiplies an N by NRHS matrix X by a symmetric tridiagonal
*  matrix A and stores the result in a matrix B.  The operation has the
*  form
*
*     B := alpha * A * X + beta * B
*
*  where alpha may be either 1. or -1. and beta may be 0., 1., or -1.
*
*  Arguments
*  =========
*
*  N       (input) INTEGER
*          The order of the matrix A.  N >= 0.
*
*  NRHS    (input) INTEGER
*          The number of right hand sides, i.e., the number of columns
*          of the matrices X and B.
*
*  ALPHA   (input) REAL
*          The scalar alpha.  ALPHA must be 1. or -1.; otherwise,
*          it is assumed to be 0.
*
*  D       (input) REAL array, dimension (N)
*          The n diagonal elements of the tridiagonal matrix A.
*
*  E       (input) REAL array, dimension (N-1)
*          The (n-1) subdiagonal or superdiagonal elements of A.
*
*  X       (input) REAL array, dimension (LDX,NRHS)
*          The N by NRHS matrix X.
*
*  LDX     (input) INTEGER
*          The leading dimension of the array X.  LDX >= max(N,1).
*
*  BETA    (input) REAL
*          The scalar beta.  BETA must be 0., 1., or -1.; otherwise,
*          it is assumed to be 1.
*
*  B       (input/output) REAL array, dimension (LDB,NRHS)
*          On entry, the N by NRHS matrix B.
*          On exit, B is overwritten by the matrix expression
*          B := alpha * A * X + beta * B.
*
*  LDB     (input) INTEGER
*          The leading dimension of the array B.  LDB >= max(N,1).
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ONE, ZERO
      PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I, J
*     ..
*     .. Executable Statements ..
*
      IF( N.EQ.0 )
     $   RETURN
*
*     Multiply B by BETA if BETA.NE.1.
*
      IF( BETA.EQ.ZERO ) THEN
         DO 20 J = 1, NRHS
            DO 10 I = 1, N
               B( I, J ) = ZERO
   10       CONTINUE
   20    CONTINUE
      ELSE IF( BETA.EQ.-ONE ) THEN
         DO 40 J = 1, NRHS
            DO 30 I = 1, N
               B( I, J ) = -B( I, J )
   30       CONTINUE
   40    CONTINUE
      END IF
*
      IF( ALPHA.EQ.ONE ) THEN
*
*        Compute B := B + A*X
*
         DO 60 J = 1, NRHS
            IF( N.EQ.1 ) THEN
               B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J )
            ELSE
               B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) +
     $                     E( 1 )*X( 2, J )
               B( N, J ) = B( N, J ) + E( N-1 )*X( N-1, J ) +
     $                     D( N )*X( N, J )
               DO 50 I = 2, N - 1
                  B( I, J ) = B( I, J ) + E( I-1 )*X( I-1, J ) +
     $                        D( I )*X( I, J ) + E( I )*X( I+1, J )
   50          CONTINUE
            END IF
   60    CONTINUE
      ELSE IF( ALPHA.EQ.-ONE ) THEN
*
*        Compute B := B - A*X
*
         DO 80 J = 1, NRHS
            IF( N.EQ.1 ) THEN
               B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J )
            ELSE
               B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) -
     $                     E( 1 )*X( 2, J )
               B( N, J ) = B( N, J ) - E( N-1 )*X( N-1, J ) -
     $                     D( N )*X( N, J )
               DO 70 I = 2, N - 1
                  B( I, J ) = B( I, J ) - E( I-1 )*X( I-1, J ) -
     $                        D( I )*X( I, J ) - E( I )*X( I+1, J )
   70          CONTINUE
            END IF
   80    CONTINUE
      END IF
      RETURN
*
*     End of SLAPTM
*
      END