DTBT06
Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
November 2006
November 2006
Purpose
DTBT06 computes a test ratio comparing RCOND (the reciprocal
condition number of a triangular matrix A) and RCONDC, the estimate
computed by DTBCON. Information about the triangular matrix A is
used if one estimate is zero and the other is non-zero to decide if
underflow in the estimate is justified.
condition number of a triangular matrix A) and RCONDC, the estimate
computed by DTBCON. Information about the triangular matrix A is
used if one estimate is zero and the other is non-zero to decide if
underflow in the estimate is justified.
Arguments
| RCOND |
(input) DOUBLE PRECISION
The estimate of the reciprocal condition number obtained by
forming the explicit inverse of the matrix A and computing RCOND = 1/( norm(A) * norm(inv(A)) ). |
| RCONDC |
(input) DOUBLE PRECISION
The estimate of the reciprocal condition number computed by
DTBCON. |
| UPLO |
(input) CHARACTER
Specifies whether the matrix A is upper or lower triangular.
= 'U': Upper triangular = 'L': Lower triangular |
| DIAG |
(input) CHARACTER
Specifies whether or not the matrix A is unit triangular.
= 'N': Non-unit triangular = 'U': Unit triangular |
| N |
(input) INTEGER
The order of the matrix A. N >= 0.
|
| KD |
(input) INTEGER
The number of superdiagonals or subdiagonals of the
triangular band matrix A. KD >= 0. |
| AB |
(input) DOUBLE PRECISION array, dimension (LDAB,N)
The upper or lower triangular band matrix A, stored in the
first kd+1 rows of the array. The j-th column of A is stored in the j-th column of the array AB as follows: if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd). |
| LDAB |
(input) INTEGER
The leading dimension of the array AB. LDAB >= KD+1.
|
| WORK |
(workspace) DOUBLE PRECISION array, dimension (N)
|
| RAT |
(output) DOUBLE PRECISION
The test ratio. If both RCOND and RCONDC are nonzero,
RAT = MAX( RCOND, RCONDC )/MIN( RCOND, RCONDC ) - 1. If RAT = 0, the two estimates are exactly the same. |