Annotation of rpl/lapack/lapack/dlagtm.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DLAGTM( TRANS, N, NRHS, ALPHA, DL, D, DU, X, LDX, BETA,
! 2: $ B, LDB )
! 3: *
! 4: * -- LAPACK auxiliary routine (version 3.2) --
! 5: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 6: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 7: * November 2006
! 8: *
! 9: * .. Scalar Arguments ..
! 10: CHARACTER TRANS
! 11: INTEGER LDB, LDX, N, NRHS
! 12: DOUBLE PRECISION ALPHA, BETA
! 13: * ..
! 14: * .. Array Arguments ..
! 15: DOUBLE PRECISION B( LDB, * ), D( * ), DL( * ), DU( * ),
! 16: $ X( LDX, * )
! 17: * ..
! 18: *
! 19: * Purpose
! 20: * =======
! 21: *
! 22: * DLAGTM performs a matrix-vector product of the form
! 23: *
! 24: * B := alpha * A * X + beta * B
! 25: *
! 26: * where A is a tridiagonal matrix of order N, B and X are N by NRHS
! 27: * matrices, and alpha and beta are real scalars, each of which may be
! 28: * 0., 1., or -1.
! 29: *
! 30: * Arguments
! 31: * =========
! 32: *
! 33: * TRANS (input) CHARACTER*1
! 34: * Specifies the operation applied to A.
! 35: * = 'N': No transpose, B := alpha * A * X + beta * B
! 36: * = 'T': Transpose, B := alpha * A'* X + beta * B
! 37: * = 'C': Conjugate transpose = Transpose
! 38: *
! 39: * N (input) INTEGER
! 40: * The order of the matrix A. N >= 0.
! 41: *
! 42: * NRHS (input) INTEGER
! 43: * The number of right hand sides, i.e., the number of columns
! 44: * of the matrices X and B.
! 45: *
! 46: * ALPHA (input) DOUBLE PRECISION
! 47: * The scalar alpha. ALPHA must be 0., 1., or -1.; otherwise,
! 48: * it is assumed to be 0.
! 49: *
! 50: * DL (input) DOUBLE PRECISION array, dimension (N-1)
! 51: * The (n-1) sub-diagonal elements of T.
! 52: *
! 53: * D (input) DOUBLE PRECISION array, dimension (N)
! 54: * The diagonal elements of T.
! 55: *
! 56: * DU (input) DOUBLE PRECISION array, dimension (N-1)
! 57: * The (n-1) super-diagonal elements of T.
! 58: *
! 59: * X (input) DOUBLE PRECISION array, dimension (LDX,NRHS)
! 60: * The N by NRHS matrix X.
! 61: * LDX (input) INTEGER
! 62: * The leading dimension of the array X. LDX >= max(N,1).
! 63: *
! 64: * BETA (input) DOUBLE PRECISION
! 65: * The scalar beta. BETA must be 0., 1., or -1.; otherwise,
! 66: * it is assumed to be 1.
! 67: *
! 68: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
! 69: * On entry, the N by NRHS matrix B.
! 70: * On exit, B is overwritten by the matrix expression
! 71: * B := alpha * A * X + beta * B.
! 72: *
! 73: * LDB (input) INTEGER
! 74: * The leading dimension of the array B. LDB >= max(N,1).
! 75: *
! 76: * =====================================================================
! 77: *
! 78: * .. Parameters ..
! 79: DOUBLE PRECISION ONE, ZERO
! 80: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
! 81: * ..
! 82: * .. Local Scalars ..
! 83: INTEGER I, J
! 84: * ..
! 85: * .. External Functions ..
! 86: LOGICAL LSAME
! 87: EXTERNAL LSAME
! 88: * ..
! 89: * .. Executable Statements ..
! 90: *
! 91: IF( N.EQ.0 )
! 92: $ RETURN
! 93: *
! 94: * Multiply B by BETA if BETA.NE.1.
! 95: *
! 96: IF( BETA.EQ.ZERO ) THEN
! 97: DO 20 J = 1, NRHS
! 98: DO 10 I = 1, N
! 99: B( I, J ) = ZERO
! 100: 10 CONTINUE
! 101: 20 CONTINUE
! 102: ELSE IF( BETA.EQ.-ONE ) THEN
! 103: DO 40 J = 1, NRHS
! 104: DO 30 I = 1, N
! 105: B( I, J ) = -B( I, J )
! 106: 30 CONTINUE
! 107: 40 CONTINUE
! 108: END IF
! 109: *
! 110: IF( ALPHA.EQ.ONE ) THEN
! 111: IF( LSAME( TRANS, 'N' ) ) THEN
! 112: *
! 113: * Compute B := B + A*X
! 114: *
! 115: DO 60 J = 1, NRHS
! 116: IF( N.EQ.1 ) THEN
! 117: B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J )
! 118: ELSE
! 119: B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) +
! 120: $ DU( 1 )*X( 2, J )
! 121: B( N, J ) = B( N, J ) + DL( N-1 )*X( N-1, J ) +
! 122: $ D( N )*X( N, J )
! 123: DO 50 I = 2, N - 1
! 124: B( I, J ) = B( I, J ) + DL( I-1 )*X( I-1, J ) +
! 125: $ D( I )*X( I, J ) + DU( I )*X( I+1, J )
! 126: 50 CONTINUE
! 127: END IF
! 128: 60 CONTINUE
! 129: ELSE
! 130: *
! 131: * Compute B := B + A'*X
! 132: *
! 133: DO 80 J = 1, NRHS
! 134: IF( N.EQ.1 ) THEN
! 135: B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J )
! 136: ELSE
! 137: B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) +
! 138: $ DL( 1 )*X( 2, J )
! 139: B( N, J ) = B( N, J ) + DU( N-1 )*X( N-1, J ) +
! 140: $ D( N )*X( N, J )
! 141: DO 70 I = 2, N - 1
! 142: B( I, J ) = B( I, J ) + DU( I-1 )*X( I-1, J ) +
! 143: $ D( I )*X( I, J ) + DL( I )*X( I+1, J )
! 144: 70 CONTINUE
! 145: END IF
! 146: 80 CONTINUE
! 147: END IF
! 148: ELSE IF( ALPHA.EQ.-ONE ) THEN
! 149: IF( LSAME( TRANS, 'N' ) ) THEN
! 150: *
! 151: * Compute B := B - A*X
! 152: *
! 153: DO 100 J = 1, NRHS
! 154: IF( N.EQ.1 ) THEN
! 155: B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J )
! 156: ELSE
! 157: B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) -
! 158: $ DU( 1 )*X( 2, J )
! 159: B( N, J ) = B( N, J ) - DL( N-1 )*X( N-1, J ) -
! 160: $ D( N )*X( N, J )
! 161: DO 90 I = 2, N - 1
! 162: B( I, J ) = B( I, J ) - DL( I-1 )*X( I-1, J ) -
! 163: $ D( I )*X( I, J ) - DU( I )*X( I+1, J )
! 164: 90 CONTINUE
! 165: END IF
! 166: 100 CONTINUE
! 167: ELSE
! 168: *
! 169: * Compute B := B - A'*X
! 170: *
! 171: DO 120 J = 1, NRHS
! 172: IF( N.EQ.1 ) THEN
! 173: B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J )
! 174: ELSE
! 175: B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) -
! 176: $ DL( 1 )*X( 2, J )
! 177: B( N, J ) = B( N, J ) - DU( N-1 )*X( N-1, J ) -
! 178: $ D( N )*X( N, J )
! 179: DO 110 I = 2, N - 1
! 180: B( I, J ) = B( I, J ) - DU( I-1 )*X( I-1, J ) -
! 181: $ D( I )*X( I, J ) - DL( I )*X( I+1, J )
! 182: 110 CONTINUE
! 183: END IF
! 184: 120 CONTINUE
! 185: END IF
! 186: END IF
! 187: RETURN
! 188: *
! 189: * End of DLAGTM
! 190: *
! 191: END
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