# ctbt06.f - Man Page

TESTING/LIN/ctbt06.f

## Synopsis

### Functions/Subroutines

subroutine **ctbt06** (rcond, rcondc, uplo, diag, n, kd, ab, ldab, rwork, rat)**CTBT06**

## Function/Subroutine Documentation

### subroutine ctbt06 (real rcond, real rcondc, character uplo, character diag, integer n, integer kd, complex, dimension( ldab, * ) ab, integer ldab, real, dimension( * ) rwork, real rat)

**CTBT06**

**Purpose:**

CTBT06 computes a test ratio comparing RCOND (the reciprocal condition number of a triangular matrix A) and RCONDC, the estimate computed by CTBCON. 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.

**Parameters***RCOND*RCOND is REAL 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*RCONDC is REAL The estimate of the reciprocal condition number computed by CTBCON.

*UPLO*UPLO is CHARACTER Specifies whether the matrix A is upper or lower triangular. = 'U': Upper triangular = 'L': Lower triangular

*DIAG*DIAG is CHARACTER Specifies whether or not the matrix A is unit triangular. = 'N': Non-unit triangular = 'U': Unit triangular

*N*N is INTEGER The order of the matrix A. N >= 0.

*KD*KD is INTEGER The number of superdiagonals or subdiagonals of the triangular band matrix A. KD >= 0.

*AB*AB is COMPLEX 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*LDAB is INTEGER The leading dimension of the array AB. LDAB >= KD+1.

*RWORK*RWORK is REAL array, dimension (N)

*RAT*RAT is REAL 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.

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **124** of file **ctbt06.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page ctbt06(3) is an alias of ctbt06.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK